Update production deployment section

[dennisvang]

fixes #57
fixes #104

[dennisvang]

To prevent duplication and stale examples, I think it would be best to link directly to the content of the FAIRDataTeam/compose repo. This can be done with the help of the sphinx literalinclude directive, as long as we have access to the compose files during build.

There are several ways to achieve this:

• add a build step that clones the repo or pulls the relevant files into a local directory
• include the repo as a git submodule
• include the repo as a git subtree
• (perhaps link directly to files on github? not sure if this is possible with sphinx and restructuredtext)
• ...

Of these options, I think git submodule is probably the best fit, because it makes our intention very explicit.
Submodules can be tricky, but I think our use case is quite straightforward.
Moreover, readthedocs also supports submodules.

[luizbonino]

I like the idea of the submodule.