Intro and updated/moved social request info

Why is this change being made?

We recently updated and expanded the social media request issue templates for team members to request social media coverage. I updated the "requesting social promotion" section to reflect those changes.

In addition to the content of that section, I moved it up to the top of the page as an easy guide for folks looking for this info. I also included a "welcome to..." section at the top as an introduction to the social handbook.

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