constructed, let users know some limitations (#84510)

* constructed, let users know some limitations

reasons https://forum.ansible.com/t/debugging-constructed-inventory-constructing-group-from-values-of-host-variables/39443

* fix indent

* Update lib/ansible/plugins/doc_fragments/constructed.py

Co-authored-by: Felix Fontein <felix@fontein.de>

* updated as per fb

---------

Co-authored-by: Felix Fontein <felix@fontein.de>

lib/ansible/plugins/doc_fragments/constructed.py

@@ -79,4 +79,8 @@ options:
     type: boolean
     default: True
     version_added: '2.11'
+notes:
+  - Inventories are not finalized at this stage, so the auto populated C(all) and C(ungrouped) groups will
+    only reflect what previous inventory sources explicitly added to them.
+  - Runtime 'magic variables' are not available during inventory construction. For example, C(groups) and C(hostvars) do not exist yet.
 """