Add Missing Content

[oubiwann]

The following need to be done:

• Create a Docs Style Guide - Create a docs style guide #53
• Add LFE Code of Conduct - Add LFE Code of Conduct #74
• Add Beginner's Guide - Add Beginner's Guide #76
• Add Developer's Guide - Add Developer's Guide #77
• Add an LFE FAQ - Add an LFE FAQ #78
• Create a basic tutorial for LFE - Create a basic tutorial for LFE #40
• Create a comprehensive LFE tutorial - Create a comprehensive LFE tutorial #42
• Installing LFE Modules - Installing LFE Modules #79
• Publishing LFE Modules/Projects - Publishing LFE Modules/Projects #80
• Create a Contributor's Guide - Create a Contributor's Guide #81
• Contribute an LFE page to "Learn X in Y Minutes" - Contribute an LFE page to "Learn X in Y Minutes" #48
• Add tutorial for rebar3 plugins - Add tutorial for rebar3 plugins #14
• Add Cookbook - Add Cookbook #11
• Add Cheatsheet - Add Cheatsheet #10

Part of release #95

[oubiwann]

We're going to ditch the docs site with all serious content going into LFE books, and general docs content going to lfe.io/docs