Add note about patching Glade 2.12 to compile it with newer GTK versions.

git-svn-id: https://geany.svn.sourceforge.net/svnroot/geany/trunk@5762 ea778897-0a13-0410-b9d1-a72fbfd435f5

HACKING

@@ -126,6 +126,15 @@ installed on the system.
 You can download Glade 2.12.2 here:
 http://download.geany.org/glade-2.12.2.tar.gz
 
+On recent GTK versions, you need a small patch to make it compile.
+You can get the patch from:
+http://download.geany.org/glade-2.12.2-build-fixes.patch
+
+And then simply apply it like so::
+
+    $ /tmp/glade-2.12.2% patch -p1 < glade-2.12.2-build-fixes.patch
+
+
 GTK API documentation
 ---------------------
 The official GTK 2.8 API documentation is not available online anymore,