Move PromptWorks dotfile repo to ~/.promptworks-dotfiles

Since we expect the custom dotfiles in ~/.dotfiles, it doesn't seem to
make much sense to have the PromptWorks dotfiles in a totally other
location.

Plus, it's much easier to remember where they are when they are in your
home directory.
Merge pull request #9 from promptworks/move-local-repo

Move PromptWorks dotfile repo to ~/.promptworks-dotfiles