Setup 'git activity' as custom command

1. Save the file in a folder in your PATH. The file must be named just like the custom command you want. In this case, the command we want is git activity, so the file must be named git-activity.

2. The file must be executable, so probably you'll need this:

   $ chmod +x /path/to/git-activity

3. Restart your console and the command should be ready to use as git activity

   $ git activity