Tweak man page for ghc command

This commit updates the ghc command's man page as followings:

* Enable `man_show_urls` to show URL addresses in the `DESCRIPTION`
section of ghc.rst, because sphinx currently removes hyperlinks
for man pages.

* Add a `SEE ALSO` section to point to the GHC homepage

docs/users_guide/conf.py

@@ -135,7 +135,7 @@ man_pages = [
 ]
 
 # If true, show URL addresses after external links.
-#man_show_urls = False
+man_show_urls = True
 
 
 # -- Options for Texinfo output -------------------------------------------

docs/users_guide/ghc.rst

@@ -379,3 +379,8 @@ Copyright
 
 Copyright 2015. The University Court of the University of Glasgow.
 All rights reserved.
+
+See also
+--------
+
+https://www.haskell.org/ghc     the GHC homepage