Add note to Matrix->Telegram EDU bridging

ROADMAP.md

@@ -6,9 +6,9 @@
   * [x] Message edits
   * [ ] ‡ Message history
   * [x] Presence
-  * [x] Typing notifications
-  * [x] Read receipts
-  * [x] Pinning messages
+  * [x] Typing notifications*
+  * [x] Read receipts*
+  * [x] Pinning messages*
   * [x] Power level
     * [x] Normal chats
       * [ ] Non-hardcoded PL requirements
@@ -56,5 +56,6 @@
   * [ ] ‡ Secret chats (not yet supported by Telethon)
   * [ ] ‡ E2EE in Matrix rooms (not yet supported 
 
+\* Requires [double puppeting](https://github.com/tulir/mautrix-telegram/wiki/Authentication#replacing-telegram-accounts-matrix-puppet-with-matrix-account) to be enabled  
 † Information not automatically sent from source, i.e. implementation may not be possible  
 ‡ Maybe, i.e. this feature may or may not be implemented at some point