LocalVisage: Add Docker instructions

[Larsluph]

Add working Dockerfile and docker-compose project file.

Update README as well with instructions on how to switch.

[Nonoty]

Oh nice ! I changed the description saying it wasn't possible but you did it :)

[Larsluph]

I just added a side note for anyone using a reverse proxy.

Not sure if an alternative is possible using the stash plugin API to add some sort of forward mechanism.
This would remove the need of having custom redirections and delegate all logic to the plugin itself.