Added missing choice of version in the docker deployment guide

docs/installation/docker.rst

@@ -17,7 +17,9 @@ Create your env file:
 
 .. parsed-literal::
 
+    export FUNKWHALE_VERSION="|version|"
     curl -L -o .env "https://code.eliotberriot.com/funkwhale/funkwhale/raw/|version|/deploy/env.prod.sample"
+    sed -i "s/FUNKWHALE_VERSION=latest/FUNKWHALE_VERSION=$FUNKWHALE_VERSION/" .env
 
 Ensure to edit it to match your needs (this file is heavily commented)