This PR is intended to work in concert with the discourse_docker changes
in https://github.com/discourse/discourse_docker/pull/292. I have used
those changes to build a local "discourse_dev" image, and then
_**these**_ changes to easily spin up and work on Discourse and plugin
functionality. It's working well for me, but of course YMMV.
Add `--init` and `--patch` options to bin/docker/boot_dev to make it
easier to spin up a container running Discourse out of a development
directory.
Add `bin/docker/README.md` to explain how to go about using the docker
command-line tools.
Tweak the Docker command-line tools to use the `-u` option to specify
user rather than changing to the user "inside" the container via `chpst`
(This way, we don't have to explicitly specify the HOME environment
variable, either.)
Add `bin/docker/shell` command to make it easy to jump inside the
running container.
