Sets up commit signing for Github in Linux/Windows
This script does the following:
- Creates a new SSH key (If a key doesn't already exist)
- Adds the key to SSH agent (If not already added)
- Enables SSH for Git globally
- Enables the SSH signing key for Git globally
- Enables Git commit signing globally
- Gives instructions on how to register the SSH key as a signing key and optionally as an authentication key on Github