docs: changed root readme (#24)

Author: oljekechoro

README.md

@@ -1,6 +1,35 @@
 # Buildstamp monorepo
+Utility for generating buildstamp file, which contains build meta info like gitcommit hash, timestamp, repo name and so on. This file could be a part of some release artifact (npm-package, docker-image) and makes it self-descriptive.
+```json
+{
+  "git": {
+    "commitId": "fc6e78b11ef4c7db1c8b89fa6b0d9b3ad4ad481d",
+    "repoName": "qiwi/buildstamp.git",
+    "repoUrl": "https://github.com/qiwi/buildstamp.git"
+  },
+  "docker": {
+    "imageTag": "foo"
+  },
+  "date": "2020-08-27T20:47:41.958Z"
+}
+```
 ## Packages
-### core
-Package with buildstamp utility and API
-### binaries
-Buildstamp utility executables for different platforms
+### [buildstamp](https://github.com/qiwi/buildstamp/tree/master/packages/core)
+Buildstamp generator utility supporting native JS and CLI API
+```javascript
+import { execute } from 'buildstamp'
+
+const stamp = execute({
+    git: true,
+    date: { format: 'iso' },
+    docker: { imageTag: 'foo' }
+})
+```
+```shell script
+buildstamp --out.path=some/path/b.json --git --docker.imageTag=foo --date.format=iso
+```
+###  [buildstamp-bin](https://github.com/qiwi/buildstamp/tree/master/packages/bin)
+Buildstamp generator executables for MacOS, Windows and Linux. They don't need Node.js for executing.
+```shell script
+./buildstamp-macos --out.path=some/path/b.json --git --docker.imageTag=foo --date.format=iso
+```