Installation docs incomplete

[retpoline]

First, great project!

Some feedback though. It would ease the unnecessary learning curve for folks who come across this project and are like "what is phoenix? what is mix? how do I get this thing setup?", etc.

Adding some basics to the docs around how to actually use this thing on a computer, such apt-get install erlang elixir, mix local hex, .... would be very helpful to know ahead of time for initial setup.

[GriffinMB]

Thanks for opening this issue! I'll add some links to the appropriate projects (e.g Elixir, Phoenix) to clarify the process

[retpoline]

That would be greatly appreciated-- it seems debian based systems are common enough to share some apt install instructions if possible, along with any modifications needed.