Filling out the commands to run for tasks

[srfraser]

Currently most of the documentation has us log in to buildbot-master85 and copy/paste some commands and environment variables.

However, we could:

1. Add a release task --show 2 firefox 61.0b5 style command
2. Which looks up the graphids/revision/current step from the json in rw-data
3. Uses that to fill out a template for a command to run including all the Task IDs and ACTION_FLAVOR
4. Prints it for copy/pasting.

If there was a read-only copy of releasewarrior and releasewarrior-data on the execution host, it could also run the command itself.

This might also be useful migration work for fully automating the steps, and making them click-to-go in shipit v2