docs/management-bundles: add hint that S3 regional endpoint should b…

…e used (open-policy-agent#4196)

Global endpoints lead to 307 responses until they're fully provisioned;
that in turn causes the Authorization header to not be forwarded, and
the GET request thus fails.

Signed-off-by: Dan Oliver <dan.oliver@iress.com>

docs/content/management-bundles.md

@@ -525,6 +525,8 @@ bundles:
     resource: bundle.tar.gz
 ```
 
+**NOTE:** the S3 `url` is the bucket's regional endpoint.
+
 ##### Metadata Credentials
 
 In order for this to work it is required that the permissions you created in the "Authentication" steps above are embedded in an IAM Role, which is then assigned to the EC2 instance hosting OPA.
@@ -545,6 +547,8 @@ bundles:
     resource: bundle.tar.gz
 ```
 
+**NOTE:** the S3 `url` is the bucket's regional endpoint.
+
 ### Google Cloud Storage
 
 #### OPA Bundle Support