Docs: Update notes for checking code

Author: GaryJones

Diff for: .github/CONTRIBUTING.md

@@ -20,6 +20,12 @@ When contributing please ensure you follow the guidelines below so that we can k
 - When committing, reference your issue (if present) and include a note about the fix.
 - Push the changes to your fork and submit a pull request to the 'develop' branch of the ... repository.
 
+### Checking You Changes
+
+- Run unit tests: `phpunit`
+- Run mutation tests: `infection` (see `logs/infection.log`)
+- Run code standards: `composer phpcs`
+
 ## Code Documentation
 
 - Please make sure that every method is documented well and the documentation follows the standards.