Added OBS setup and livestream instructions

Why is this change being made?

Clarifying configuration and setup for an open source option for live streaming to our YouTube channel. Also trying to follow https://about.gitlab.com/handbook/communication/#numbering-is-for-reference-not-as-a-signal

Does this MR meet the acceptance criteria?

Conformity

• Added description to this MR explaining the reasons for the proposed change, per say-why-not-just-what