Update learning and other resources

[nickserv]

• Learning
  • Remove out of date recommendations
    • Anything suggesting ES6 is the latest syntax is probably too confusing
    • Dan's container component article (not useless but generally not recommended by most any more thanks to hooks/redux/etc)
  • Add doc links
  • Updated best practices
• Get to the point where the site is more of an all-around resource both to learning React stuff and using Reactiflux effectively while following the rules
• Make sure meta pages are up to date
• Consider moving useful information from Reactiflux itself (pins, channel descriptions, bot commands) to the website for easier discoverability and permalinking