Update docs for next release

[alichtman]

• Updated functionality, usage info and user guide in README
  • Detailed --add and --rm tutorial
• Warn people against sharing files with sensitive info on accident.
• Remove "NOTE: shallow-backup works best when it's populating an empty directory." from README
• Move "Featured On" to below "Inspiration" and update TOC
• Travis CI Badge
• Remove Use Cases
• Updated CHANGELOG
• New gif demo to show all current features
• Incr to v2.0

[alichtman]

Gif Demo:

$ pip install setup.py
$ shallow-backup
# Show new git repo initialized and created dir
set up remote
back up dotfiles
# it'll commit and push
$ shallow-backup -old_path
back up packages
# it'll commit and push
$ exit