Update azure_rm_virtualmachine.py (#45325)

* Update azure_rm_virtualmachine.py

A lot of Azure images are not cloud-init ready and need to be prepared manually before attempting to use the custom_data option of this module. Adding a line to the description to make others aware. If, like me, they are used to working with AWS AMIs that all seem to have cloud-init baked in, this could prevent some troubleshooting as to why their custom_data scripts aren't running in Azure.

* fixing addition to azure_rm_virtualmachine.py

* Update azure_rm_virtualmachine.py

* final update

* fixed url syntax

* nuked trailing whitespace

lib/ansible/modules/cloud/azure/azure_rm_virtualmachine.py

@@ -29,6 +29,10 @@ description:
     - Before Ansible 2.5, this required an image found in the Azure Marketplace which can be discovered with
       M(azure_rm_virtualmachineimage_facts). In Ansible 2.5 and newer, custom images can be used as well, see the
       examples for more details.
+    - If you need to use the I(custom_data) option, many images in the marketplace are not cloud-init ready. Thus, data
+      sent to I(custom_data) would be ignored. If the image you are attempting to use is not listed in
+      U(https://docs.microsoft.com/en-us/azure/virtual-machines/linux/using-cloud-init#cloud-init-overview),
+      follow these steps U(https://docs.microsoft.com/en-us/azure/virtual-machines/linux/cloudinit-prepare-custom-image).
 
 options:
     resource_group: