Update the plotTimeSeries documentation for new setup

[lmoureaux]

Description

Fixes #130

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Motivation and Context

From #130:

Current Behavior

Documentation still references git-based commands, such as "vi $GEM_PLOTTING_PROJECT/mapping/chamberInfo.py", which are no longer in use. This does not make it clear which copy of chamberInfo.py the user should change.

Expected Behavior

Documentation should reference paths within venv, and make it clear that the files to be used/changed should be within the user's virtual environment, i.e. "vi /path/to/your/venv/slc6/py2.7/lib/python2.7/site-packages/gempython/gemplotting/mapping/chamberInfo.py"

Checklist:

• [x] My code follows the code style of this project.
• [x] My change requires a change to the documentation.
• [x] I have updated the documentation accordingly.
• [ ] I have added tests to cover my changes.
• [ ] All new and existing tests passed.