add top level documentation about not expecting already encoded URI's
//!
//! If needed, the request will be re-issued to a temporary redirect endpoint. This can happen with
//! newly created S3 buckets not in us-standard/us-east-1.
+//!
+//! Please note that this module does not expect URIs to already be encoded.
+//!
use std::borrow::Cow;
use std::collections::btree_map::Entry;
