Add config.toml as a mapped file instead of copying

This should reduce the number of rebuilds that we have to do for a
simple configuration change

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

docker-compose.yml

@@ -6,4 +6,5 @@ services:
       - "./omnibot:/app/omnibot"
       - "./plugins:/app/plugins"
       - "./data:/app/data"
+      - "./config.toml:/app/config.toml"
     restart: unless-stopped