📝(compose) Increase attachment upload size to 10 MB

Mostly give this as an example how a person deploying this knows which
knob to turn.

Signed-off-by: Luca Weiss <luca@lucaweiss.eu>

docker/files/production/etc/nginx/conf.d/default.conf.template

@@ -11,6 +11,9 @@ server {
     server_name localhost;
     charset utf-8;
 
+    # increase max upload size
+    client_max_body_size 10m;
+
     # Disables server version feedback on pages and in headers
     server_tokens off;