Add a note to iosxr_(command|config|facts) stating netconf is not supported

lib/ansible/modules/network/iosxr/iosxr_command.py

@@ -27,6 +27,7 @@ description:
     Please use M(iosxr_config) to configure iosxr devices.
 extends_documentation_fragment: iosxr
 notes:
+  - This module does not support netconf connection
   - Tested against IOS XR 6.1.2
 options:
   commands:

lib/ansible/modules/network/iosxr/iosxr_config.py

@@ -26,6 +26,7 @@ description:
 extends_documentation_fragment: iosxr
 notes:
   - Tested against IOS XRv 6.1.2
+  - This module does not support netconf connection
   - Avoid service disrupting changes (viz. Management IP) from config replace.
   - Do not use C(end) in the replace config file.
 options:

lib/ansible/modules/network/iosxr/iosxr_facts.py

@@ -25,6 +25,9 @@ description:
     module will always collect a base set of facts from the device
     and can enable or disable collection of additional facts.
 extends_documentation_fragment: iosxr
+notes:
+  - Tested against IOS XRv 6.1.2
+  - This module does not support netconf connection
 options:
   gather_subset:
     description: