docs: Fix missing usage in the nav

Author: pawamoy

docs/usage.md

@@ -1,3 +1,7 @@
+!!! tip "This is the documentation for the LEGACY Python handler."
+    To read the documentation for the NEW, EXPERIMENTAL handler,
+    go to the [new handler documentation](https://mkdocstrings.github.io/python).
+
 ## Handler options
 
 Like every handler, the Python handler accepts the common

mkdocs.yml

@@ -8,6 +8,7 @@ site_dir: "site"
 nav:
 - Home:
   - Overview: index.md
+  - Usage: usage.md
   - Changelog: changelog.md
   - Credits: credits.md
   - License: license.md

src/mkdocstrings/handlers/python/collector.py

@@ -120,7 +120,7 @@ def collect(self, identifier: str, config: dict) -> CollectorItem:
 
         Then we pick up the only object within the `objects` list (there's always only one, because we collect
         them one by one), rebuild it's categories lists
-        (see [`rebuild_category_lists()`][mkdocstrings.handlers.python.rebuild_category_lists]),
+        (see [`rebuild_category_lists()`][mkdocstrings.handlers.python.collector.rebuild_category_lists]),
         and return it.
 
         Arguments: