docs: note behavior w 2 providers

crates/providers/src/layers/nonce.rs

@@ -17,7 +17,10 @@ use std::marker::PhantomData;
 ///
 /// # Note
 ///
-/// If the transaction request does not have a sender set, this layer will not fill nonces.
+/// - If the transaction request does not have a sender set, this layer will not fill nonces.
+/// - Using two providers with their own nonce layer can potentially fill invalid nonces if
+///   transactions are sent from the same address, as the next nonce to be used is cached internally
+///   in the layer.
 ///
 /// # Example
 ///