Clarify how to add yourself to team page
- Move duplicated initial steps from each method for adding yourself to the team page into a simplified pre-task checklist.
- Extract picture image requirements to a list for easier reading.
- Convert git-page-update index file to support ERB.
- Deduplicate instructions on what fields shoud be modified in the team member data YAML by moving them into a partial.
- Removes old placeholder for Robert Marshall.
Closes #2997 (closed)