docstring and readme update for RCS messages

Author: maxkahan

README.md

@@ -212,15 +212,18 @@ client.messages.send_message({
 
 ### Revoke an RCS Message
 
+To mark a WhatsApp message as read, you must override the default `vonage.Client.api_host` attribute. Override it to correspond to the region where the WhatsApp number you're using is hosted.
+
 ```python
+# Override api_host attribute for EU region
+client.api_host('api-eu.vonage.com')
+
 client.messages.revoke_outbound_message('MY-MESSAGE-ID')
 ```
 
 ### Send an audio file via WhatsApp
 
-You will need a WhatsApp Business Account to use WhatsApp messaging. WhatsApp restrictions mean that you
-must send a template message to a user if they have not previously messaged you, but you can send any message
-type to a user if they have messaged your business number in the last 24 hours.
+You will need a WhatsApp Business Account to use WhatsApp messaging. WhatsApp restrictions mean that you must send a template message to a user if they have not previously messaged you, but you can send any message type to a user if they have messaged your business number in the last 24 hours.
 
 ```python
 client.messages.send_message({

src/vonage/messages.py

@@ -54,6 +54,12 @@ def send_message(self, params: dict):
     def revoke_outbound_rcs_message(self, message_uuid: str) -> None:
         """Revoke an outbound RCS message.
 
+        Note: to use this method, update the `api_host` attribute of the `vonage.Client` instance
+        to the API endpoint corresponding to the region where the WhatsApp number is hosted.
+
+        For example, to use the EU API endpoint, set the `api_host`
+        attribute to 'api-eu.vonage.com'.
+
         Args:
             message_uuid (str): The UUID of the message to revoke.
         """
@@ -71,7 +77,7 @@ def mark_whatsapp_message_read(self, message_uuid: str) -> None:
         to the API endpoint corresponding to the region where the WhatsApp number is hosted.
 
         For example, to use the EU API endpoint, set the `api_host`
-        attribute to 'https://api-eu.vonage.com'.
+        attribute to 'api-eu.vonage.com'.
 
         Args:
             message_uuid (str): The UUID of the message to mark as read.