Create CONTRIBUTING.md

Establishing Contribution expectations.

CONTRIBUTING.md

@@ -0,0 +1,11 @@
+Contributing
+============
+
+To ease code reviews please follow the [PSR-1](http://www.php-fig.org/psr/1/) and
+[PSR-2](http://www.php-fig.org/psr/2/). Take a few minutes to actually read them,
+they're not all that bad. To jump right in use the [PHP-CS-Fixer
+tool](http://cs.sensiolabs.org/). Or install PHP_CodeSniffer and use it like so:
+
+`apt install php-codesniffer`
+
+`phpcs --standard=PSR2 your_file.php`