Add docker compose for mkdocs deployment

[CBroz1]

In my previous PR, I failed to realize the .gitignore excluded the docs docker compose. Here, I

• Add a line to the gitignore to permit this compose file specifically
• Add a docker compose file, which works in my local deployment

Note: tests will fail, as this is not the staging branch. I'm PRing here because of the precedent set by the previous docs PR