Add documentation for -t switch for tests.

GettingStarted.wiki

diff --git a/GettingStarted.wiki b/GettingStarted.wiki
index da73121..2ce3b44 100644
--- a/GettingStarted.wiki
+++ b/GettingStarted.wiki
@@ -63,6 +63,26 @@
 bin/run-tests
 }}}
 
+This will run, by default, all types of tests. This is the same as running
+
+{{{
+bin/run-tests -t js,pyunit
+}}}
+
+So, using {{{ -t }}} switch it's possible to choose a list of comma-separated types of tests to run.
+
+To run only pyunit tests:
+
+{{{
+bin/run-tests -t pyunit
+}}}
+
+To run only js tests:
+
+{{{
+bin/run-tests -t js
+}}}
+
 = Checking Out the Code =
 
 To check out Melange source code run the following command: