Update new and old READMEs

[NicEastvillage]

• Mark https://github.com/RLBot/RLBot as outdated (maybe even rename the repo to *v4 so core can take its name?)
  • PR: Update README and mark as deprecated RLBot#668
• Mark https://github.com/RLBot/RLBotGUI as outdated (maybe even rename the repo to *v4 so gui can take its name?)
  • Update README and mark as deprecated RLBotGUI#250
• Make sure READMEs of new repos are done
  • Basic information about the project
  • Setup instructions
  • Maintenance/contribution instructions
  • Deployment instructions
  • Repos:
    • https://github.com/RLBot/flatbuffers-schema
    • Bridge
    • https://github.com/RLBot/core/
    • https://github.com/RLBot/gui
• Update website
  • PR: Prepare website for v5 release rlbot.github.io#72

[VirxEC]

I like the repo names "core" and "gui" - but I do agree that the old v4 repos should eventually be marked as such in the READMEs.

[NicEastvillage]

It is just a bit strange that we are distributing binaries called RLBotServer and rlbotgui while the similarly named RLBot and RLBotGUI repos are different outdated projects.