Add KOSS Communication Platform Guides & Mention The Archive

[harshkhandeparkar]

There is no single guide about which communication platforms KOSS uses. The onboarding doc mentions the platforms.

Since we use a lot of platforms now - Slack, WhatsApp, Google Group, we should have a separate document listing all the platforms and guidelines for how to use each (eg, Slack for official communication, Google Group for something that needs to be broadcast to everyone, etc.). Guidelines for setting up meetings can also be included in this as Google Meet is also used often.

Lastly, the slack archive: https://opsa.kossiitkgp.org, should also be mentioned so it is documented and maintained in the future.