docs: Update Guide to Learning Cohorts

[meg-gutshall]

Summary

Update file here: https://github.com/Virtual-Coffee/VC-Contributors/blob/main/coffee-table-groups/guides/guide-to-learning-cohorts.md

Context

I think we need documentation around Virtual Coffee's Learning Cohorts and how to successfully hold one. Right now, there isn't much documented since we've only held one so far!

Goals

I would like to document some standard procedures, such as promoting via the #learning-together Slack channel and using our Technical Resources category in GitHub Discussions.

Then I would like to collect some tips and lessons learned from past Learning Cohort Leads. This should include things they thought went well, things they wished they had done differently, and what someone can reasonably expect when hosting a VC Learning Cohort.

Lastly, I'd like to list previous Learning Cohorts with their Leads and link them back to the GitHub Discussions.

Resources

This was a wealth of information to pull from: https://github.com/orgs/Virtual-Coffee/discussions/493

Collaborators

@virtualandy and @wheeleruniverse – I would love your contributions here!!