Bring repo up-to-date

[fkrause98]

There are some things we have to do in order to bring the erlings repo up to date, there are some things I've come up with:

• Use GitHub actions, replace badge with Github CI badge. #77
• Add an up-to-date install Erlang setup with asdf, nix or both. #78
• Make sure we're using rebar3 everywhere. #79
• Update install step readme to show the proper output, right now it's showing up something old.. #80
• Upgrade deprecated modules #81
• Do the erlings from 0 and write down everything out-of-date we find, ideally someone with a non-erlang background should do every exercise #82
  the exercises eventually since the goal of this repo is to teach Erlang.