docs: note about apparmor

docs/operators/handbook.md

@@ -248,6 +248,10 @@ usermod -aG docker $USER
 # setup swarm
 docker swarm init
 docker network create -d overlay proxy
+
+# on debian machines as of 2023-02-17
+apt install apparmor
+systemctl restart docker containerd
 ```
 
 `abra` will do this for you when you run `abra server add --provision`.