Add initial contributor guide

Fix typo in contribute.rst

This completes the work required to merge PR #211 (corresponding to issue #202)
also included as part of issue #194.

in response to note #211 (comment)

This primarily fixes first/second person style (relating to issue #202).

Following up on PR #211 and issue #202.

The unescaped asterisk causes a warning when building the docs and has
unintended formatting consequences.

This adds a naive test of whether the docs are sound: whether the build
completes without warnings. To get sphinx-build to return an exit status
of 1 on errors, the flag to promote warnings to errors is set.

virtualenv guide: Fix link

…n-packaging-user-guide into JoshuaAcosta-prerequisites

This is for issue #196 and PR #214.