Reflect discussion in (nested / hard-to-find) issue: https://github.com/gaul/s3proxy/issues/783 in the wiki.

Storage-backend-examples.md

@@ -144,6 +144,10 @@ jclouds.credential=xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
 jclouds.endpoint=https://objects.dreamhost.com
 ```
 
+When pointing jclouds to a generic S3 API (`jclouds.provider=s3`), jclouds uses [AWSSIGV2](https://docs.aws.amazon.com/AmazonS3/latest/API/Appendix-Sigv2.html) authentication by default. AWSSIGV2 is deprecated and may not be supported by S3 providers like Cloudflare R2 (e.g. https://github.com/gaul/s3proxy/issues/783). 
+
+You may override the the jclouds default to make it use AWSSIGV4 by setting `jclouds.s3.signer-version=4` (https://issues.apache.org/jira/browse/JCLOUDS-1594). However, this may not work for PUT requests for certain S3 providers (e.g. https://github.com/gaul/s3proxy/issues/783).
+
 ### Swift (non-Keystone)
 
 outdated?!