Change config.cfg comment regarding ec2 spot option (#14345)

Reference the documentation to know the proper IAM permissions

Author: glennschler

config.cfg

@@ -184,9 +184,8 @@ cloud_providers:
       name: "ubuntu-focal-20.04"
       arch: x86_64
       owner: "099720109477"
-    # Change instance_market_type from "on-demand" to "spot" to take advantage of
-    # simplified spot launch options
-    # See https://aws.amazon.com/blogs/compute/new-amazon-ec2-spot-pricing/
+    # Change instance_market_type from "on-demand" to "spot" to launch a spot
+    # instance. See deploy-from-ansible.md for spot's additional IAM permission
     instance_market_type: on-demand
   gce:
     size: e2-micro