Document or delete top-level docs_prev directory

[eecavanna]

I noticed this top-level directory today. I searched the repository for the string "docs_prev" and did not find any occurrences outside of the docs_prev directory, itself. Also, the directory was last updated 3 years ago.

Things I'm wondering:

1. Does "prev" stand for "previous" and was the directory created because someone wanted to archive old documentation before creating new documentation?
2. What value, if any, is this directory providing to anyone? Is it being used by anything that anyone knows of?
3. Does anyone object to this directory being deleted (given that it would continue to exist in the Git history)?

I will assign to @dwinston as Git shows him as the only editor of this directory:

Task:

• Either add a note to README.md saying what that directory is, or delete the directory