added documentation

Author: quickliketurtle

doc/rate_limits.md

@@ -0,0 +1,23 @@
+## Rate Limit API
+[Back to the navigation](README.md)
+
+Get Rate Limit
+Wraps [GitHub Rate Limit API](http://developer.github.com/v3/rate_limit/).
+
+#### Get All Rate Limits.
+
+```php
+$rateLimits = $github->api('rate_limit')->getRateLimits();
+```
+
+#### Get Core Rate Limit
+
+```php
+$coreLimit = $github->api('rate_limit')->getCoreLimit();
+```
+
+#### Get Search Rate Limit
+
+```php
+$searchLimit = $github->api('rate_limit)->getSearchLimit');
+```