docs: add copy tracking design doc to MkDocs

Missed in #3574.

mkdocs.yml

@@ -9,7 +9,7 @@ theme:
   features:
     # - navigation.top
 
-  # Respect the users default settings and add a toggle for manually choosing 
+  # Respect the user's default settings and add a toggle for manually choosing
   # automatic/light/dark palette.
   # taken from https://squidfunk.github.io/mkdocs-material/setup/changing-the-colors/#system-preference
   palette:
@@ -131,11 +131,10 @@ nav:
       - 'Design Docs': 'design_docs.md'
       - 'Design Doc Blueprint': 'design_doc_blueprint.md'
 
-- 'Design docs': 
+- 'Design docs':
     - 'git-submodules': 'design/git-submodules.md'
     - 'git-submodule-storage': 'design/git-submodule-storage.md'
     - 'JJ run': 'design/run.md'
     - 'Sparse Patterns v2': 'design/sparse-v2.md'
     - 'Tracking branches': 'design/tracking-branches.md'
-
-
+    - 'Copy tracking and tracing': 'design/copy-tracking.md'