Clarify scope of packaging tutorial.
Distributions -> Distribution Packages for titles

"Python Distributions" already refers to things like ActivePython, Anaconda, EPD, Canopy and Python(x, y), so switching to the less ambiguous "Distribution Packages" for these section titles.
Incorporate comments from @qwcode on the pull request.

This commit is part of pull request #105:

https://github.com/pypa/python-packaging-user-guide/pull/105
Merge pull request #105 from cjerdonek/clarify-scope

Clarify scope of packaging tutorial
Minor bugfix: pip user flag was missing a dash

Signed-off-by: Daniel Farrell <dfarrell@redhat.com>
Merge pull request #109 from dfarrell07/master

Minor bugfix: pip user flag was missing a dash
Batch of minor grammar bugfixes

Signed-off-by: Daniel Farrell <dfarrell@redhat.com>
Merge pull request #110 from dfarrell07/master

Batch of minor grammar bugfixes