Document that fig rm removes volumes

[bfirsh]

It's not immediately clear that you will lose all of your data when running fig rm. This should be really clear.

[ChrisChinchilla]

#dibs

[albers]

Does compose really remove volumes? Docker does not, see moby/moby@00f2fd1

[bfirsh]

Hm. Good point. I guess the data is difficult to recover because you have to figure out what directory it was in. :)

[thaJeztah]

docker rm -v will also remove the volume, I think docker-compose rm -v does the same?

Note that there is discussion in Docker to make -v a requirement; ie, Docker will refuse to delete a container with volumes if rm is called without -v