Add README describing this package.

README.md

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+# babybird
+[![NPM][NPM1]][NPM2]
+
+[![Build Status][1]][2] [![dependency status][3]][4] [![dev dependency status][5]][6]
+
+A very fast standards-compliant [ES2015] Promise library for node.
+
+There are several fast promise implementations out there, like
+[`bluebird`], but they all add a bunch of stuff that's not in the
+[ES2015] Promise spec.  Further, as they've added more and more
+features they've grown so complex that they can't be easily audited
+against the ES2015 spec (or the official `test262` test suite).
+
+The `babybird` library is a stripped-down "just ES2015" Promise
+implementation, which passes the Promises/A+ and `test262` test
+suites.  It is very competitive with the performance of [`bluebird`],
+without having to give us standards compliance.  On the doxbee
+benchmark running under node 5.1.0, `babybird` is 2.4 times faster
+than native Promises, 4 times faster than the Promise implementation
+in [`core-js`], and almost 9 times faster than the Promise
+implementation in [`es6-shim`].  The performance improvement is even
+greater when running under node 0.10.
+
+Further, `babybird` supports subclassing (as all ES2015 Promise
+implementations ought).  This means that if you'd like additional
+bells and whistles on your Promises, you can add then via subclassing
+and without stomping on the global Promise.  In fact, the [`prfun`]
+library provides much the same feature set as `bluebird`, but with a
+clean separation of concerns.  Further, `prfun` runs on top of *any*
+ES2015-compliant Promise implementation, so if `babybird` is someday
+supplanted, you can just swap out the core Promise implementation
+underneath `prfun` without having to update any of your uses of the
+core ES2015 or extended `prfun` API.
+
+## Usage
+```
+npm install babybird
+```
+
+```javascript
+var Promise = require('babybird');
+```
+
+The `babybird` library plays very nicely with [`prfun`], if you'd like
+a few bells and whistles with your library.  I recommend creating a
+new module, named (say) `promise.js`, with the contents:
+```javascript
+module.exports = require('prfun/wrap')(require('babybird'));
+```
+and then using the wrapped promises this way:
+```javascript
+var Promise = require('./promise.js');
+```
+
+## Benchmarks
+These benchmarks are derived from the benchmarks included with
+`bluebird`.  A few of the bluebird test cases have been forked to
+add "fair" versions, since bluebird obtained some of its speed by
+using a faster `promisify` method than that provided to other
+promise implementations, and by using a few `bluebird`-specific
+APIs which appeared to be tuned for the benchmark.
+
+You can reproduce these results using `npm run bench`.
+
+### Node 0.10
+```
+results for 20000 parallel executions, 1 ms per I/O op
+
+file                                         time(ms)  slowdown  memory(MB)
+callbacks-baseline.js                             819      0.48  32.99
+promises-bluebird.js                             1383      0.81  50.59
+promises-bluebird-fair.js                        1715      1.00  39.02
+promises-cscott-babybird-noall.js                1870      1.09  41.19
+promises-cscott-babybird.js                      1925      1.12  61.81
+promises-cscott-babybird-prfun.js                1991      1.16  48.60
+promises-then-promise-es6.js                     3084      1.80  64.54
+promises-then-promise.js                         3112      1.81  64.39
+promises-paulmillr-es6shim.js                   12475      7.27  94.20
+promises-zloirock-corejs.js                     18695     10.90  94.11
+
+Platform info:
+Linux 4.2.0-1-amd64 ia32
+Node.JS 0.10.40
+V8 3.14.5.9
+Intel(R) Core(TM) i7 CPU       L 640  @ 2.13GHz × 4
+```
+
+### Node 5.1.0
+```
+results for 20000 parallel executions, 1 ms per I/O op
+
+file                                         time(ms)  slowdown  memory(MB)
+callbacks-baseline.js                             826      0.53  29.29
+promises-bluebird-generator.js                   1105      0.71  25.49
+promises-bluebird-generator-fair.js              1113      0.72  28.27
+promises-cscott-babybird-prfun-generator.js      1202      0.77  33.68
+promises-bluebird-fair.js                        1553      1.00  51.38
+promises-cscott-babybird-noall.js                1623      1.05  65.25
+promises-bluebird.js                             1643      1.06  43.66
+promises-cscott-babybird-prfun.js                1707      1.10  72.33
+promises-cscott-babybird.js                      1724      1.11  72.82
+promises-then-promise-es6.js                     2985      1.92  106.96
+promises-then-promise.js                         3004      1.93  106.69
+promises-ecmascript6-native.js                   3770      2.43  176.96
+promises-zloirock-corejs.js                      6298      4.06  155.89
+promises-paulmillr-es6shim.js                   13892      8.95  227.61
+
+Platform info:
+Linux 4.2.0-1-amd64 ia32
+Node.JS 5.1.0
+V8 4.6.85.31
+Intel(R) Core(TM) i7 CPU       L 640  @ 2.13GHz × 4
+```
+
+## License
+
+Copyright (c) 2015 C. Scott Ananian
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
+
+[ES2015]:     http://www.ecma-international.org/ecma-262/6.0/
+[`bluebird`]: https://github.com/petkaantonov/bluebird
+[`es6-shim`]: https://github.com/paulmillr/es6-shim
+[`core-js`]:  https://github.com/zloirock/core-js
+[`prfun`]:    https://github.com/cscott/prfun
+
+[NPM1]: https://nodei.co/npm/babybird.png
+[NPM2]: https://nodei.co/npm/babybird/
+
+[1]: https://travis-ci.org/cscott/babybird.png
+[2]: https://travis-ci.org/cscott/babybird
+[3]: https://david-dm.org/cscott/babybird.png
+[4]: https://david-dm.org/cscott/babybird
+[5]: https://david-dm.org/cscott/babybird/dev-status.png
+[6]: https://david-dm.org/cscott/babybird#info=devDependencies