Fix function signatures for parse_change_desc.

At some point we added a parameter to this method, but perforce_vmware.py was
never updated as such. Trivial fix.

Reviewed at https://reviews.reviewboard.org/r/6453/
Add a document on reviewing text files.

2.0.x includes a text file review UI, which syntax highlights based on the
mimetype and allows adding comments to each line, much like the diff viewer.
While we were shipping the feature, we never had any documentation about it.

Testing done:
Built and checked html docs.

Reviewed at https://reviews.reviewboard.org/r/6452/
Merge branch 'release-2.0.x'