Updating instructions on contributions

This links to the newly created online ICLA form.

CONTRIBUTING.md

@@ -1,16 +1,30 @@
-# Guidelines for contributing
+# Contributing to OpenLayers
 
-## Code formatting
+Thanks for your interest in contributing to OpenLayers development.  Our
+preferred means of receiving contributions is through [pull
+requests](https://help.github.com/articles/using-pull-requests).
+
+Before accepting a contribution, we ask that you provide us a Contributor
+License Agreement.  If you are making your contribution as part of work for
+your employer, please follow the guidelines on submitting a [Corporate
+Contributor License Agreement](http://www.openlayers.org/ccla.txt).  If you are
+making your contribution as an individual, you can submit a digital
+[Individual Contributor License Agreement](https://docs.google.com/spreadsheet/viewform?formkey=dGNNVUJEMXF2dERTU0FXM3JjNVBQblE6MQ).
+
+## Coding guidelines
+
+### Formatting
 
 We use the [Closure
-Linter](https://developers.google.com/closure/utilities/docs/linter_howto) for
-checking JavaScript files for style issues. To execute the linter use:
+Linter](https://developers.google.com/closure/utilities/docs/linter_howto) to
+check source files for potential syntax and coding style issues. To execute the
+linter run the following after making your changes:
 
     $ make lint
 
 This command assumes that the `gjslint` command in on your PATH.
 
-## Code compilation
+### Compilation
 
 The OpenLayers 3 is compiled and type-checked using the [Closure
 Compiler](https://developers.google.com/closure/compiler/). To
@@ -18,19 +32,19 @@ compile the code use:
 
     $ make build-all
 
-## Generating doc
+### Documentation
 
 We use [jsdoc3](https://github.com/jsdoc3/jsdoc) to generate the API
-doc. Changing the code can break the generation of the API
-doc. Use the following to generate the doc:
+documentation.  To ensure that your changes are properly documented (and don't
+break API doc generation), run the following:
 
     $ make doc
 
 This command assumes that the `jsdoc` command is on your PATH.
 
-## Tests
+### Testing
 
-Changes should not break existing tests. We use
+Any modifications must not break existing tests. We use
 [PhantomJS](http://phantomjs.org/) to run tests *headlessly*.
 Use the following to run the tests:
 
@@ -38,7 +52,7 @@ Use the following to run the tests:
 
 This command assumes that the `phantomjs` command is on your PATH.
 
-## The `precommit` target
+### The `precommit` target
 
 The Makefile includes a `precommit` target for running all of the
 above (`lint`, `build-all`, `doc`, and `test`). As the name of the
@@ -47,7 +61,7 @@ committing:
 
     $ make precommit
 
-## Commit messages
+### Commit messages
 
 We follow http://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html
 for the formatting of commit messages.