index: Add info about having fallen out of support

manual-build @ 9c8161c1

-Subproject commit edba682faea4ef588c5539c66ccbb17570aed5a0
+Subproject commit 9c8161c1be95fe35714d2c32f7e9fc7402ef50d4

source/index.rst

@@ -6,7 +6,12 @@
 Mahara 17.04 user manual
 ==================================
 
-This is the user manual for Mahara 17.04, which was released on 27 April 2017. When you see the "New in Mahara 17.04" icon |new in Mahara 17.04|, a feature was introduced in Mahara 17.04 or changed from Mahara 16.10.
+This is the user manual for Mahara 17.04, which was released on 27 April 2017.
+
+.. warning::
+   Mahara 17.04 is not supported any more as of October 2018. Please install or upgrade to a `supported version of Mahara <https://wiki.mahara.org/index.php/SupportedVersions>`_.
+
+When you see the "New in Mahara 17.04" icon |new in Mahara 17.04|, a feature was introduced in Mahara 17.04 or changed from Mahara 16.10.
 
 .. note::