Additional support statements in ROSA docs

Author: mletalie

modules/rosa-getting-support.adoc

@@ -17,6 +17,10 @@ If you experience difficulty with a procedure described in this documentation, v
 .. Complete the remaining fields.
 .. On the _Review_ page, select the correct cluster ID that you are contacting support about, and click `Submit`.
 
-You can also get support from link:https://aws.amazon.com/premiumsupport/[AWS Support] as long as you have a valid AWS support contract.
+You can also get support from link:https://aws.amazon.com/premiumsupport/[AWS Support] as long as you have a valid AWS Support contract and have enabled AWS Business, Enterprise On-Ramp, or Enterprise support plans.
+
+To enable an AWS Support plan, see link:http://aws.amazon.com/premiumsupport/knowledge-center/sign-up-support/[How do I sign up for an AWS Support plan?]
+
+For information about creating an AWS Support case, see the link:https://docs.aws.amazon.com/awssupport/latest/user/case-management.html[AWS support case] documentation.
 
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