Create SSH keygen script to (hopefully) prevent confusion in the future

The SSH keygen script can be CURL'd and piped to bash to generate an ed25519 SSH key. It works as follows

• check if a key with the name id_25519 already exists. If so, print out the contents of the public key.
• Ask the user to enter an E-mail address
• Run ssh-keygen with this E-mail address, the default output filename and the type ed25519\
• Run eval $( ssh-agent -s )
• Run ssh-add with this new key
• Print out the contents of the new public key

The SSH setup has been a point of confusion for many attendees (as most people don't understand the commands they're typing), and this is an attempt to make this step less complex.