Update disk-container file path param for custom RHCOS AMI imports

Author: codyhoag

modules/installation-aws-upload-custom-rhcos-ami.adoc

@@ -78,7 +78,7 @@ EOF
 ----
 $ aws ec2 import-snapshot --region ${AWS_DEFAULT_REGION} \
      --description "<description>" \ <1>
-     --disk-container <file_path>/containers.json <2>
+     --disk-container "file://<file_path>/containers.json" <2>
 ----
 <1> The description of your {op-system} disk being imported, like
 `rhcos-${RHCOS_VERSION}-x86_64-aws.x86_64`.