Make man page show up in apropos

Set the 'description' attribute so that Sphinx builds the manpage with
the 'NAME' section. This is necessary for `apropos` to be able to find
yamllint

Fixes part of #76

docs/conf.py

@@ -39,7 +39,7 @@ htmlhelp_basename = 'yamllintdoc'
 # One entry per manual page. List of tuples
 # (source start file, name, description, authors, manual section).
 man_pages = [
-    ('index', 'yamllint', '', [u'Adrien Vergé'], 1)
+    ('index', 'yamllint', 'Linter for YAML files', [u'Adrien Vergé'], 1)
 ]
 
 # -- Build with sphinx automodule without needing to install third-party libs