Add documentation on our testing environment

[annakrystalli]

Given our last submissions have issues with the automated tests with respect to our testing environment, I'm wondering if we might be able to help the situation with a little more transparency regarding the testing environment we use. I suggest a section in our devguide with:

• a bit more detail about the testing environment, perhaps just show the dockerfile used to build the image for testing.
• some guidance on how to identify missing dependencies and also what to do if author's identify missing dependencies (either let us know or make a pull request themselves?)
• perhaps add a checkbox to the submission template also.

In any case, transparency over both what we have available and any additional dependencies installed could also benefit reviewers who might also hit issues at times with local installations.

Related to #587