docs: Update documentation to include solution to potential problems with gtk module on OS X

Change-Id: Ib6a46b64bff07c3aa3e799a7490b45ba22fa4c4f
diff --git a/docs/source/faq.rst b/docs/source/faq.rst
index cad083a..71cb2cb 100644
--- a/docs/source/faq.rst
+++ b/docs/source/faq.rst
@@ -138,6 +138,26 @@
 Something is wrong with your python bindings and python bindings dependencies.  Please follow
 the :ref:`requirements` section that lists what should be installed in order to run visualizer.
 
+.. _Problems with the gtk python module on OS X:
+
+Problems with the gtk python module on OS X
+-------------------------------------------
+
+.. topic:: ./waf configure got stuck during the gtk module check
+
+    When running ``./waf configure``, the process freezes at the stage of detecting gtk module::
+
+      ...
+      Checking for 'sqlite3'                                         : yes
+      Checking for header linux/if_tun.h                             : not found
+      Checking for python module 'gtk'                               :
+
+If ``./waf configure`` on OSX got stuck during the gtk python module check, it most likely
+means that something is wrong with X11 required by this module.  You can try to reinstall X11
+(`XQuartz <http://xquartz.macosforge.org>`_) or configure NS-3 without python bindings (``./waf
+configure --disable-python``).  Note that disabling python bindings will also disable the
+visualizer module.
+
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