Add civilint page

docs/tools/civilint.md

+Civilint is a thin wrapper which calls jshint and PHP_CodeSniffer (with the 
+coder ruleset).
+
+Code-style tests ensure a consistent layout across all of the codebase, and 
+they also identify some unsafe or confusing coding patterns. While working on a 
+patch, you should run civilint to determine if the pending changes comply with 
+style guides. 
+
+Note that civilint may be invoked a few different ways:
+
+```bash
+civilint # (no arguments) – Check style of any uncommitted changes.
+civilint some/file.php # Check style of a specific file (or list of files).
+git diff --name-only origin/4.6.. | civilint - # Check changed files
+```
+
+See also:
+
+- [CiviCRM Coding Standards](https://wiki.civicrm.org/confluence/display/CRMDOC/PHP+Code+and+Inline+Documentation)
+- [CiviCRM Javascript Standards](https://wiki.civicrm.org/confluence/display/CRMDOC/Javascript+Reference)
+- [Drupal Coding Standards](https://www.drupal.org/docs/develop/standards/coding-standards)
+- [PHP_CodeSniffer](https://github.com/squizlabs/PHP_CodeSniffer)
+- [coder](https://github.com/civicrm/coder)
+- [jshint](http://jshint.com/)