Running Rustfmt from Atom

You'll need to install Beautify, you can do this by running apm install atom-beautify.

There are 2 setting that need to be configured in the atom beautifier configuration.

Install rustfmt as per the readme.
Open the atom beautifier settings

Go to Edit->Preferences. Click the packages on the left side and click on setting for atom-beautifier
Set rustfmt as the beautifier

Find the setting labeled Language Config - Rust - Default Beautifier and make sure it is set to rustfmt as shown below. You can also set the beautifier to auto format on save here.
Set the path to your rustfmt location

Find the setting labeled Rust - Rustfmt Path. This setting is towards the bottom and you will need to scroll a bit. Set it to the path for your rustfmt executable.