Simplify bootstrapping

[phodge]

pip3 install homely --user && homely add ... is too hard, especially if pip3/python3 aren't already installed.

• Getting homely into the main brew/yum/apt repos might help. If we do this, the bootstrapping command could be brew install homely && homely add <url>

• Another solution would be to include a tool which compiles a custom shell script which is committed to the user's dotfiles repo such that they can use curl raw.githubusercontent.com/user/dotfiles/master/install.sh | sh

Also, we should make an easy way to put the bootstrapping instructions in the user's README.md so they can copy+paste from there easily.

Other things we could do to help the user along:

• automatically switch on cloning via ssh if ssh to github.com works ... see https://help.github.com/articles/testing-your-ssh-connection/
• swap a github repo to the ssh path automatically if we know we can: https://help.github.com/articles/changing-a-remote-s-url/