Merge pull request #4612 from mitchellh/fix4553

document how aws-sdk uses the shared credentials file

website/source/docs/builders/amazon.html.md

@@ -78,8 +78,11 @@ following steps:
 
 2.  Look for [local AWS configuration
     files](https://docs.aws.amazon.com/cli/latest/userguide/cli-chap-getting-started.html#cli-config-files)
-    -   First `~/.aws/credentials`
-    -   Next based on `AWS_PROFILE`
+    - Looks for the credentials file in the `AWS_SHARED_CREDENTIALS_FILE`
+      environment variable, and if that's empty, use the default credentials
+      file (`.aws/credentials`) in the user's home directory.
+    - Uses the profile name set in the `AWS_PROFILE` environment variable. If
+      the environment variable is not set, uses "default" as the profile name.
 
 3.  Lookup an IAM role for the current EC2 instance (if you're running in EC2)