README: import from default track README (#334)

Before:
https://github.com/exercism/request-new-language-track/blob/53b185fdc67f0e5e7bc2b0891c2a1cb30e4b5f05/README.md

After:
https://github.com/exercism/request-new-language-track/blob/master/TRACK_README.md

(current sha is 907c3210b89bbc49c04ffa85f3b71f51cd9f8c1c)
https://github.com/exercism/request-new-language-track/blob/907c3210b89bbc49c04ffa85f3b71f51cd9f8c1c/TRACK_README.md

Closes #287

README.md

@@ -5,10 +5,91 @@
 
 Exercism exercises in Rust
 
-## Contributing Guide
+## Contributing
 
-Please see the [contributing guide](https://github.com/exercism/docs/tree/master/contributing-to-language-tracks)
+Thank you so much for contributing! :tada:
 
+Please read about how to [get involved in a track](https://github.com/exercism/docs/tree/master/contributing-to-language-tracks). Be sure to read the Exercism [Code of Conduct](https://github.com/exercism/exercism.io/blob/master/CODE_OF_CONDUCT.md).
+
+We welcome pull requests of all kinds. No contribution is too small.
+
+We encourage contributions that provide fixes and improvements to existing exercises. Please note that this track's exercises must conform to the Exercism-wide standards described in the [documentation](https://github.com/exercism/docs/tree/master/language-tracks/exercises). If you're unsure about how to make a change, then go ahead and open a GitHub issue, and we'll discuss it.
+
+## Exercise Tests
+
+At the most basic level, Exercism is all about the tests. You can read more about how we think about test suites in [the Exercism documentation](https://github.com/exercism/docs/blob/master/language-tracks/exercises/anatomy/test-suites.md).
+
+Test files should use the following format:
+
+```
+extern crate exercise_name;
+
+use exercise_name::*;
+
+#[test]
+fn test_descriptive_name() {
+    assert_eq!(exercise_function(1), 1);
+}
+
+#[test]
+#[ignore]
+fn test_second_and_past_tests_ignored() {
+    assert_ne!(exercise_function(1), 2);
+}
+```
+
+## Opening an Issue
+
+If you plan to make significant or breaking changes, please open an issue so we can discuss it first. If this is a discussion that is relevant to more than just the Rust track, please open an issue in [exercism/discussions](https://github.com/exercism/discussions/issues).
+
+## Submitting a Pull Request
+
+Pull requests should be focused on a single exercise, issue, or conceptually cohesive change. Please refer to Exercism's [pull request guidelines](https://github.com/exercism/docs/blob/master/contributing/pull-request-guidelines.md).
+
+Please follow the coding standards for Rust.  [rustfmt](https://github.com/nrc/rustfmt) may help with this
+and can be installed with `cargo install rustfmt`.
+
+### Verifying your Change
+
+Before submitting your pull request, you'll want to verify the changes in two ways:
+
+* Run all the tests for the Rust exercises
+* Run an Exercism-specific linter to verify the track
+
+All the tests for Rust exercises can be run from the top level of the repo with `_test/check-exercises.sh`. If you are on a Windows machine, there are additional [Windows-specific instructions](_test/WINDOWS_README.md) for running this.
+
+For the Exercism-specific linting, please see [the documentation](https://github.com/exercism/docs/blob/master/language-tracks/configuration/linting.md).
+
+## Contributing a New Exercise
+
+Please see the documentation about [adding new exercises](https://github.com/exercism/docs/blob/master/you-can-help/make-up-new-exercises.md).
+
+Note that:
+
+- Each exercise must stand on its own. Do not reference files outside the exercise directory. They will not be included when the user fetches the exercise.
+
+- Exercises must conform to the Exercism-wide standards described in [the documentation](https://github.com/exercism/docs/tree/master/language-tracks/exercises).
+
+- Each exercise should have:
+
+      exercises/exercise-name/
+                              tests/exercise-name.rs  <- a test suite
+                              src/lib.rs              <- an empty file or with exercise stubs
+                              example.rs              <- example solution that satisfies tests
+                              Cargo.toml              <- with version equal to exercise defintion
+                              Cargo.lock              <- Auto generated
+                              README.md               <- Instructions for the exercise (see notes below)
+
+- The stub file and test suite should use only the Rust core libraries. `Cargo.toml` should not list any external dependencies as we don't want to make the student assume required crates. If an `example.rs` uses external crates, include `Cargo-example.toml` so that `_tests/check-exercises.sh` can compile with these when testing.
+
+- If porting an existing exercise from problem-specifications that has a `canonical-data.json` file, use the version in `canonical-data.json` for that exercise as your `Cargo.toml` version.  Otherwise, use "0.0.0".
+
+- An exercise may contain `.meta/hints.md`.  This is optional and will appear after the normal exercise
+  instructions if present.  Rust is different in many ways from other languages.  This is a place where the differences required for Rust are explained.  If it is a large change, you may want to call this out as a comment at the top of `src/lib.rs`, so the user recognises to read this section before starting.
+
+- `README.md` may be [regenerated](https://github.com/exercism/docs/blob/master/maintaining-a-track/regenerating-exercise-readmes.md) from Exercism data. The generator will use the `description.md` from the exercise directory in the [problem-specifications repository](https://github.com/exercism/problem-specifications/tree/master/exercises), then any hints in `.meta/hints.md`, then the [Rust-specific instructions](https://github.com/exercism/rust/blob/master/config/exercise-readme-insert.md). The `## Source` section comes from the `metadata.yml` in the same directory.  Convention is that the description of the source remains text and the link is both name and hyperlink of the markdown link.
+
+- Be sure to add the exercise to an appropriate place in the `config.json` file.  The position in the file determines the order exercises are sent.   Generate a unique UUID for the exercise.  Current difficuly levels in use are 1, 4, 7 and 10.
 
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