Add a basic CONTRIBUTING guide

CONTRIBUTING.md

@@ -0,0 +1,30 @@
+# Contributing to the Rust-Buildbot infrastructure
+
+Thank you for your interest in contributing to our infrastructure! The
+workflow for this project is similar to, but simpler than, that of the [Rust
+language][rust].
+
+## Making Changes
+
+Submit your changes as a pull request to this repository. If there's a
+specific contributor who should review the change, mention them with `r?
+@theirname` in the body of your commit message. 
+
+The rust-highfive bot will take a look at your PR and make sure you have a
+reviewer. 
+
+After all of the reviewer's concerns have been addressed, anyone with
+permissions can merge your PR.  
+
+## Testing Changes
+
+If you're an enterprising contributor who'd like to spin up your very own
+intsance of rust-buildbot for any reason, we need your help! 
+
+It isn't easy to run your own rust-buildbot for testing changes (or any other
+reason) right now, but we're working on it! If you have any specific
+complaints about why contributing to this project is hard, please file issues
+about them or comment about them on [this issue][issue]!
+
+[rust]: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md
+[issue]: https://github.com/rust-lang/rust-buildbot/issues/15