Update links in README so they work on docker hub

README.md

@@ -3,12 +3,12 @@ A Matrix-Telegram hybrid puppeting/relaybot bridge.
 
 ### [Wiki](https://github.com/tulir/mautrix-telegram/wiki)
 
-### [Features & Roadmap](ROADMAP.md)
+### [Features & Roadmap](https://github.com/tulir/mautrix-telegram/blob/master/ROADMAP.md)
 
 ## Discussion
 Matrix room: [`#telegram:maunium.net`](https://matrix.to/#/#telegram:maunium.net)
 
 Telegram chat: [`mautrix_telegram`](https://t.me/mautrix_telegram) (bridged to Matrix room)
 
 ## Preview
-![Preview](preview.png)
+![Preview](https://raw.githubusercontent.com/tulir/mautrix-telegram/master/preview.png)