chore: Add description for new tag

src/openapi.yaml

@@ -97,6 +97,8 @@ tags:
     description: Personal favourites by the currently logged in user
   - name: Me / Plans
     description: Personal plans by the currently logged in user
+  - name: Me / Plans / Lectures
+    description: Manage the lectures for a plan for the logged in user
 
 paths:
   # Lecturers