S3: Add checksum configuration for Non-Amazon providers

Author: tmorrell

docs/operate/customize/file-uploads/s3.md

@@ -56,4 +56,15 @@ To enable file previews in InvenioRDM when using Amazon S3, you must configure C
         "ExposeHeaders": []
     }
 ]
+
+## Non-Amazon S3 Providers
+
+If you're using a Non-Amazon S3 provider, you may have to configure the checksum behaviour with:
+
+```
+S3_CONFIG_EXTRA = {
+        "request_checksum_calculation": "WHEN_REQUIRED",
+        "response_checksum_validation": "WHEN_REQUIRED",
+    }
+```
 ```