Added describe command to readme

Author: david

README.rst

@@ -254,6 +254,21 @@ would be default in next MAJOR release (unified differ, estimating, full-width p
 
     $ PHP_CS_FIXER_FUTURE_MODE=1 php php-cs-fixer.phar fix -v --diff
 
+Rules
+-----
+
+Use the following command to quickly understand what a rule will do to your code:
+
+.. code-block:: bash
+
+    $ php php-cs-fixer.phar describe align_multiline_comment
+
+To visualize all the rules that belong to a ruleset:
+
+.. code-block:: bash
+
+    $ php php-cs-fixer.phar describe @PSR2
+
 Choose from the list of available rules:
 
 * **align_multiline_comment** [@PhpCsFixer]

src/Console/Command/HelpCommand.php

@@ -143,6 +143,17 @@ public static function getHelpCopy()
 
     <info>$ PHP_CS_FIXER_FUTURE_MODE=1 php %command.full_name% -v --diff</info>
 
+Rules
+-----
+
+Use the following command to quickly understand what a rule will do to your code:
+
+    <info>$ php php-cs-fixer.phar describe align_multiline_comment</info>
+
+To visualize all the rules that belong to a ruleset:
+
+    <info>$ php php-cs-fixer.phar describe @PSR2</info>
+
 Choose from the list of available rules:
 
 %%%FIXERS_DETAILS%%%