Module page should list distributions that require it

[fgabolde]

So far ThisPAN only displays relationships between distributions, but the module-to-distribution relationship exists in the model.

It might be worth it to add a third tab to the module page listing the distribution rdeps, with a disclaimer that this list is likely to be incomplete (since many authors just add the main module of a distribution as a dependency, e.g. Moo and not Moo::Role).