Add GenServer snippet and README descriptions

[GoNZooo]

I added a GenServer template and some README descriptions.

[florinpatrascu]

Successfully published [email protected]!

Thank you!
:)

[GoNZooo]

Happy to help! I like the idea of having these be in a separate extension so that they can be pulled in separately if people want them. I'll be adding more in the future if I see a need. There might be a GenStateMachine, GenStage {Producer,Consumer} waiting somewhere in the future. :D

[florinpatrascu]

Totally, that’s why I started this project. It is much cleaner to chose and swap extensions containing just code snippets, than doing that while losing other functionality from an extension containing the desired functions, but not the wanted snippets. Now I wish Code had a better way of helping you turning off just the snippets from a given extension, as right now I have to manually tweak the extensions offering a subset or just incomplete set of Elixir snippets, and disable their snippets. Anyway thanks a lot for help, and please keep the snippets coming :)