Document anatomy of the Tutor root

[kdmccormick]

Context

When writing my CourseGraph plugin, I found that in order to correctly write and debug my plugin's patch files and templates, I needed to understand the significance of the files in $(tutor config printroot).

Tutor docs do a great job of describing that ./config.yml is used as input to generate ./env, but I don't think they described the other folders (./data, ./volumes) nor the internal structure of ./env.

In particular, I it took me a while to find out that:

• docker-compose commands are executed relative to $(tutor config printroot)/env/<mode>.
• Following from ^, when a data volume is bind-mounted at ../../data/<service>, that resolves to $(tutor config printroot)/data/<service>.
• Plugin templates are rendered to $(tutor config printroot)/env/plugins

Acceptance

After the Plugin API v1 is specified, ensure there are docs explaining the structure of $(tutor config printroot). Should be part of the plugin developer guide.

[regisb]

I like the fact that you are making a list of all the weird, non-intuitive things that you stumble upon and that I never think of because I have forgotten how strange they are 😉

The best way to address this issue is probably to write a "Plugin developer guide". By describing step-by-step what a plugin developer needs to do, we'll automatically discover most of the weird stuff.

[kdmccormick]

Sounds good! I'll make this a subtask within a greater Plugin Developer Guide task.