Remove Parity, Watch, Suspenders, and Rails

* These are great tools, but not critical.
* Some tools should be re-installed right before their use,
  such as Suspenders.
* Restrict Laptop to more fundamental setup.
* Document how to install these in `~/.laptop.local`.
Personal dotfiles, right? I think laptop.local is intentionally not in thoughtbot/dotfiles. If it was meant for the whole team, it'd be in Laptop. I plan on adding watch, tree, etc to my personal laptop.local in my dotfiles.

Or are you suggesting something else?