Fix osxfuse github link in installation docs

It was broken because there's already a different reference named
github in `docs/global.rst.inc`. Fixed by using an anonymous hyperlink
reference, per https://stackoverflow.com/a/14067756/278488

docs/installation.rst

@@ -230,12 +230,11 @@ dependencies::
     pip3 install virtualenv
 
 For FUSE support to mount the backup archives, you need at least version 3.0 of
-FUSE for OS X, which is available via github_, or via homebrew::
+FUSE for OS X, which is available via `github <https://github.com/osxfuse/osxfuse/releases/latest>`__,
+or via homebrew::
 
     brew cask install osxfuse
 
-.. _github: https://github.com/osxfuse/osxfuse/releases/latest
-
 
 FreeBSD
 ++++++++