[add] content to the `collections.md` file

[ll-zerr]

1. Create a Table of Contents that includes the following:

• What's in a collection
• Naming conventions for DA collections (example: CoreConcept.Aspect)
• How to create a collection
• How to rename a collection
• List of current Strapi collections relating to the Needs Assessment

2. Create sub-issues for each selection of the TOC.
3. Add links to the collections.md TOC for each selection upon completion.
4. Update the Table of Contents in the Needs Assessment readme.md file to include the collections.md TOC.