add pre-setup with some security measures

readme.md

@@ -32,9 +32,13 @@ contact ~ben or sose on tilde.chat (in the #slbr channel) to sign up.
 - jq
 - BSD style netcat (`netcat-openbsd` on debian)
 
-## Setup
+## Pre-Setup
 - Make sure your ports 1337, 1338 and 1339 are not exposed to the internet, as
   SLBR will use them internally
+- Make sure to employ user namespace remapping with docker, eg. by starting
+  dockerd with `dockerd --userns-remap=default`
+
+## Setup
 - `mkdir /home/slbr-admin`
 - `useradd slbr-admin -d /home/slbr-admin`
 - `usermod -a -G docker slbr-admin`