Added CONTRIBUTING link and documented usage of 'document-check'

Author: Benjamin Wilson Friedman

CONTRIBUTING.md

@@ -76,6 +76,10 @@ Make sure your code is linted with phpcs ([PSR-2 Coding Style]):
 You can automatically fix lint errors with phpcbf:
 
     npm run lint:fix
+    
+Finally verify that your new changes are acceptable to phpdoc:
+
+    npm run document-check
 
 The test suite is setup for code coverage if you have [XDebug] installed and setup.
 Coverage is outputted as text and as html in the phpunit-test-results/ directory within the project root.

README.md

@@ -324,7 +324,7 @@ if(ParsePush::hasStatus($response)) {
 Contributing / Testing
 ----------------------
 
-See the CONTRIBUTORS.md file for information on testing and contributing to
+See [CONTRIBUTING](CONTRIBUTING.md) for information on testing and contributing to
 the Parse PHP SDK. We welcome fixes and enhancements.
 
 [Get Composer]: https://getcomposer.org/download/