[Monolog] List available built-in formatters

Author: alexandre-daubois

logging/formatter.rst

@@ -55,3 +55,17 @@ configure your handler to use it:
                 ->formatter('monolog.formatter.json')
             ;
         };
+
+Many built-in formatters are available in Monolog. A lot of them are declared as services
+and can be used in the ``formatter`` option:
+
+* ``monolog.formatter.chrome_php``: formats a record according to the ChromePHP array format
+* ``monolog.formatter.gelf_message``: serializes a format to GELF format
+* ``monolog.formatter.html``: formats a record into an HTML table
+* ``monolog.formatter.json``: serializes a record into a JSON object
+* ``monolog.formatter.line``: formats a record into a one-line string
+* ``monolog.formatter.loggly``: formats a record information into JSON in a format compatible with Loggly
+* ``monolog.formatter.logstash``: serializes a record to Logstash Event Format
+* ``monolog.formatter.normalizer``: normalizes a record to remove objects/resources so it's easier to dump to various targets
+* ``monolog.formatter.scalar``: formats a record into an associative array of scalar (+ null) values (objects and arrays will be JSON encoded)
+* ``monolog.formatter.wildfire``: serializes a record according to Wildfire's header requirements