Suggestion: Add minimal how-to in README for git lfs
When available, `.png` and `.sketch` should be tracked by [git lfs](https://git-lfs.github.com/).

This should be as easy as doing the following steps:
1. Install git lfs onto your system
2. `git lfs install` inside of your repo
3. `git lfs track "*.png"` & `git lfs track "*.sketch"` inside of your repo

It should also be noted that your remote needs to have git lfs support.

This info is by no means critical to using this plugin, but it aids in maintaining a healthy git repo.
