README: add mediaproxy as optional requirement

- config.example.py: signal None as valid value for MEDIA_PROXY

README.md

@@ -71,7 +71,11 @@ Requirements:
 - gifsicle for GIF emoji and avatar handling
 - [pipenv]
 
+Optional requirement:
+- [mediaproxy]
+
 [pipenv]: https://github.com/pypa/pipenv
+[mediaproxy]: https://gitlab.com/litecord/mediaproxy
 
 ### Download the code
 

config.example.py

@@ -54,6 +54,7 @@ class Config:
 
     #: Mediaproxy URL on the internet
     #  mediaproxy is made to prevent client IPs being leaked.
+    #  None is a valid value if you don't want to deploy mediaproxy.
     MEDIA_PROXY = 'localhost:5002'
 
     #: Postgres credentials