Added -l

Updated Command line (markdown)

Command-line.md

@@ -52,3 +52,22 @@ In addition to the command line option, ensure you have built your code with the
 
 Usually you only want to see reporting for failed tests. Sometimes it's useful to see *all* the output (especially when you don't trust that that test you just added worked first time!).
 To see successul, as well as failing, test results just pass this option.
+
+## Listing available tests or reporters
+<pre>
+-l, --list [test|reporter] [xml]
+</pre>
+
+With no arguments this option will list all registered tests and reporters using a standard line based listing format. 
+
+Supplying the *xml* argument formats the list as an xml document (which may be useful for consumption by other tools).
+
+Supplying the *test* or *reporter* arguments narrow the list to tests or reporters respectively.
+
+Examples:
+<pre>
+-l
+-l test
+-l reporter xml
+-l xml
+</pre>