fix(docs): add models page to resolve ViewState cross-reference

docs/api/models.md

@@ -0,0 +1,3 @@
+# Models
+
+::: lonboard.models.ViewState

mkdocs.yml

@@ -60,6 +60,7 @@ nav:
   - API Reference:
       - api/viz.md
       - api/map.md
+      - api/models.md
       - Layers:
           - api/layers/bitmap-layer.md
           - api/layers/bitmap-tile-layer.md