Update dependencies, call out Pillow requirement

Author: tcpipuk

README.md

@@ -20,6 +20,7 @@ run efficiently without requiring a GPU.
 - **Python Dependencies**:
   - `beautifulsoup4`: For HTML message parsing
   - `nsfwdetection`: For image content analysis
+  - `pillow`: To read and convert images
 
 > **Important**: As well as requiring the above plugins, the default
 > Alpine-based Maubot Docker image is not compatible with `nsfwdetection`.

maubot.yaml

@@ -1,6 +1,6 @@
 maubot: 0.1.0
 id: uk.tcpip.nsfwbot
-version: 0.3.0
+version: 0.3.1
 license: AGPL-3.0-or-later
 modules:
   - nsfwbot