Create a template Rmd specifically for advanced topics/usage examples

### Background

Context is #357 - please read the initial comment for that issue in detail!

### Problem

The advanced topics notebooks have a different audience and it stands to reason that those users will have a bit more experience with things like file paths and the different platforms. We can't assume that those users have gone through our other examples (e.g., we should still treat them as independent). We should try to strike a balance between making sure folks can get up and running with refine.bio data but give more information so they can understand whether an analysis is appropriate for their question.

### What potential "gotchas" do we know of?

I expect most gotchas will become apparent while we work our way through #357. Because we want to give users an idea about whether or not an advanced approach is right for them, I'm imagining a mostly blank section in the template that's about _why_ to use an analysis.

### What are the recommended next steps?

1. Add introductory material to our first advanced topic example, which is WGCNA (#357).
2. Create a template Rmd specifically for our advanced topics examples.
3. Update CONTRIBUTING.md to reflect that there will be two templates to choose from.

Start by reading the initial comment on #357 and reviewing the first advanced-topic example, WGCNA, to understand the introductory material and template needs. Then inspect CONTRIBUTING.md and define the separate advanced-topics Rmd template. Done means the template exists, the WGCNA example has its introductory material, and CONTRIBUTING.md explains both templates.

Written by the indexing model from the issue text.