Update README.md for YAML config and other new stuff

[fndax]

Update README.md with the following changes:

• Minimum player count is now 6
• Bot configuration is now YAML-based (and also extensively commented, so I nixed a lot of the helptext previously here)
• Additional gameplay settings not in the example config file are on the wiki
• The gamemode template file went AWOL so suggest looking at existing gamemodes and the community modes instead
• Lagcheck is gone