Added a new section for package groups.
Merge branch 'pulp-2.0' into rbarlow_package_group_docs

Conflicts:
	docs/user-guide/recipes.rst
Added recipes for package groups.
Removed some Sphinx comments.
Removed >'s from the recipes file.
s/when/that.
Merge pull request #84 from pulp/rbarlow_package_group_docs

Rbarlow package group docs