chore(ci): restore blank line and add smoke test comment

Author: lucasmcdonald3

codebuild/release/validate.yml

@@ -1,4 +1,5 @@
 version: 0.2
+
 phases:
   install:
     commands:
@@ -16,6 +17,7 @@ phases:
       - |
         while [ $NUM_RETRIES -gt 0 ]
         do
+          # basic usability smoke test
           pip install "aws-encryption-sdk==$VERSION" && python -c "import aws_encryption_sdk; from aws_encryption_sdk import StrictAwsKmsMasterKeyProvider"
           if [ $? -eq 0 ]; then
             break