Add import command

[twpayne]

It's occasionally useful to unpack a tarball in to your home directory, for example to add a vim or zsh plugin.

chezmoi should have an import command that takes a tarball and unpacks it into the source directory, doing any necessary renames.

Example usage:

$ wget https://github.com/robbyrussell/oh-my-zsh/archive/master.tar.gz
$ chezmoi import --strip-components=1 master.tar.gz ~/.oh-my-zsh