Adding docker-compose.yml for simple local deployment

[markbaumgarten]

I was struggling with all of the deployment steps described and since I have my own virtual private server I found it easier for me to just:

git clone
cd
docker-compose up

Hope this might be useful for someone.

[sulkaharo]

@markbaumgarten did you notice #6903

[markbaumgarten]

@sulkaharo - No - sorry, I did not do a proper checking of current ongoing work - Perhaps I was a bit excited to be able to contribute.

Apologies for the inconvenience.