Add CI (#4)

* Added credo

* Added and ran Prettier; First pass at GH Actions

* Updated actions workflow to hopefully work on this branch

* Name the folder correctly how about

* Added proper container prefix to commands

* Apparently you have to get back into the root after commands

* CI is working, update branches to final value

mix.exs

@@ -51,7 +51,8 @@ defmodule Pinchflat.MixProject do
       {:jason, "~> 1.2"},
       {:dns_cluster, "~> 0.1.1"},
       {:plug_cowboy, "~> 2.5"},
-      {:mox, "~> 1.0", only: :test}
+      {:mox, "~> 1.0", only: :test},
+      {:credo, "~> 1.7", only: [:dev, :test], runtime: false}
     ]
   end