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

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

- [x] What's in a collection
- [x] Naming conventions for DA collections _(example: CoreConcept.Aspect)_
- [x] How to create a collection
- [x] How to rename a collection
- [x] 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.