Document running tests and linting

Add section to contributing docs detailing how to run tests and linting
on the project.

docs/contributing.md

@@ -11,6 +11,7 @@ Contents
 
 - [Workflow](#workflow)
     - [Starting a Feature Branch](#starting-a-feature-branch)
+    - [Checking your code for errors](#checking-your-code-for-errors)
     - [Submitting a Pull Request](#submitting-a-pull-request)
     - [Editing your Feature Branch](#editing-your-feature-branch)
     - [Resolving Merge Conflicts](#resolving-merge-conflicts)
@@ -76,6 +77,18 @@ you've used before.  But it's nice to have its name be somewhat
 descriptive of what it implements.
 
 
+### Checking your code for errors
+
+There's automated tests and linting setup for the project.  Please do
+add tests for any code you add and run both:
+
+    npm run test
+    npm run lint
+
+To check that your changes pass the integration tests as well as the
+ESLint rules set up for the project.
+
+
 ### Submitting a Pull Request
 
 Once you've commited changes to your feature branch that you want to