Update the intro to the contributor docs area, place Structure third

docs/contributors/architecture/introduction.md

@@ -8,3 +8,5 @@ Since most of the code in this codebase services the RSpec integration,
 these guides heavily skew toward that topic,
 and you can start with a [guide to how RSpec works if you like](./how-rspec-works.md).
 But you can also find [details around the diff engine](./how-super-diff-works.md).
+Finally, if you're curious about the files in this project and how they're organized,
+feel free to consult the [structure](./structure) document.

mkdocs.yml

@@ -29,9 +29,9 @@ nav:
       - "How to Contribute": "contributors/how-to-contribute.md"
       - Architecture:
           - "Introduction": "contributors/architecture/introduction.md"
-          - "Structure": "contributors/architecture/structure.md"
           - "How RSpec works": "contributors/architecture/how-rspec-works.md"
           - "How SuperDiff works": "contributors/architecture/how-super-diff-works.md"
+          - "Structure": "contributors/architecture/structure.md"
 
 #plugins:
 #- entangled # this also runs `entangled sync` as a pre-build action