Add a CONTRIBUTING.md file

It provides an overview of how to file a helpful issue and how to run tests.

Fixes #93

Author: fitzgen

CONTRIBUTING.md

@@ -0,0 +1,86 @@
+# Contributing to `servo/rust-bindgen`
+
+Hi! We'd love to have your contributions! If you want help or mentorship, reach
+out to us in a GitHub issue, or stop by #servo on irc.mozilla.org and introduce
+yourself.
+
+* [Code of Conduct](#coc)
+* [Filing an Issue](#issue)
+* [Building](#building)
+* [Testing](#tests)
+  * [Overview](#tests-overview)
+  * [Running All Tests](#tests-all)
+  * [Running a Single, Specific Test](#tests-one)
+  * [Authoring New Tests](#tests-new)
+
+## Code of Conduct <span id="coc"/>
+
+We abide by the [Rust Code of Conduct][coc] and ask that you do as well.
+
+[coc]: https://www.rust-lang.org/en-US/conduct.html
+
+## Filing an Issue <span id="issue"/>
+
+Think you've found a bug? File an issue! To help us understand and reproduce the
+issue, provide us with:
+
+* A reduced C/C++ header file that reproduces the issue
+* The `bindgen` flags used to reproduce the issue with the header file
+* The expected `bindgen` output
+* The actual `bindgen` output
+
+## Building <span id="building"/>
+
+Build instructions are in the [README](./README.md).
+
+## Testing <span id="tests"/>
+
+### Overview <span id="tests-overview"/>
+
+Input C/C++ test headers reside in the `tests/headers` directory. The expected
+output rust bindings live in `tests/expectations`; for example,
+`tests/headers/my_header.h`'s expected generated rust bindings would be
+`tests/expectations/my_header.rs`.
+
+The `tests/tools/run-bindgen.py` script runs `bindgen` on the test headers and
+compares the results to the expectations.
+
+### Running All Tests <span id="tests-all"/>
+
+```
+$ cargo test [--features llvm_stable]
+```
+
+This spawns a `tests/tools/run-bindgen.py` subprocess for each test header.
+
+### Running a Single, Specific Test <span id="tests-one"/>
+
+```
+$ ./tests/tools/run-bindgen.py ./target/debug/bindgen ./tests/headers/some_header.h
+```
+
+To learn more about the options available with `run-bindgen.py`:
+
+```
+$ ./tests/tools/run-bindgen.py --help
+```
+
+### Authoring New Tests <span id="tests-new"/>
+
+To add a new test header to the suite, simply put it in the `tests/headers`
+directory. Next, run the `run-bindgen.py` script with the new test header, which
+will generate the initial expected output rust bindings.
+
+If your new test requires certain flags to be passed to `bindgen`, you can
+specify them at the top of the test header, with a comment like this:
+
+```c
+// bindgen-flags: --enable-cxx-namespaces -- -std=c++14
+```
+
+If your new test requires `bindgen` to be built with certain features, you can
+specify the required features at the top of the test header in a similar manner:
+
+```c
+// bingden-features: llvm_stable
+```

README.md

@@ -76,12 +76,6 @@ $ LIBCLANG_PATH=path/to/clang-3.9/build/lib \
     cargo build
 ```
 
-## Running Tests
-
-```
-$ make test
-```
-
 # Command Line Usage
 
 There are a few options documented when running `./bindgen --help`. Other