fix example env vars in Dockerfile

Dockerfile

@@ -1,9 +1,10 @@
 FROM docker.io/python:latest
 
-ENV HOMESERVER_URL=https://matrix.org \
-    HOMESERVER_NAME=matrix.org \
-    MXID_PREFIX=snowstorm_ \
-    ADMIN_ROOM=!jaeisofjaosiefjoi:matrix.org
+ENV HOMESERVER=https://example.com \
+    MXID=@snowstorm:example.com \
+    ACCESSTOKEN_FILE=/run/secrets/accesstoken \
+    ADMIN_ROOM=!jaeisofjaosiefjoi:example.com \
+    CATEGORY=examplecategory
 
 WORKDIR /app