add contributor guide

Author: jsdf

CONTRIBUTING.md

@@ -0,0 +1,11 @@
+# Contributor Guidelines
+
+This project has automated tests which can be run with `npm test`. This will be
+run in Travis CI when you make a Pull Request so please try to ensure that they
+are passing when submitting one. If your PR adds new features please also add 
+tests. If your PR fixes a bug, it might be helpful to add a test which would fail
+if the bug was re-introduced.
+
+The source code of this project is also checked for coding errors and code style
+consistency using ESLint. You can run it with `npm run lint` to see any errors,
+and you can automatically fix some coding style errors using `npm run lint-fix`.

README.md

@@ -143,6 +143,10 @@ browserify-incremental (eg. with `--save`) to ensure that your browserify versio
 is locked by package.json, because browserify-incremental doesn't specify an 
 exact browserify version.
 
+## Contributing
+
+Please see the [Contributor Guidelines](CONTRIBUTING.md).
+
 # license
 
 MIT