aws: Add suggestion about rds_instance in rds

rds_instance is boto3 based module, add a note in rds module documentation
about the same.

Fixes: #54686

Signed-off-by: Abhijeet Kasurde <akasurde@redhat.com>

lib/ansible/modules/cloud/amazon/rds.py

@@ -17,9 +17,11 @@ module: rds
 version_added: "1.3"
 short_description: create, delete, or modify an Amazon rds instance
 description:
-     - Creates, deletes, or modifies rds instances.  When creating an instance it can be either a new instance or a read-only replica of an existing
-       instance. This module has a dependency on python-boto >= 2.5. The 'promote' command requires boto >= 2.18.0. Certain features such as tags rely
-       on boto.rds2 (boto >= 2.26.0)
+    - Creates, deletes, or modifies rds instances.
+    - When creating an instance it can be either a new instance or a read-only replica of an existing instance.
+    - This module has a dependency on python-boto >= 2.5. The 'promote' command requires boto >= 2.18.0. Certain features such as tags rely
+      on boto.rds2 (boto >= 2.26.0)
+    - Please use boto3 based M(rds_instance) instead.
 options:
   command:
     description: