updating README

README.md

@@ -5,9 +5,15 @@ Attention! it's under development, thus consider it an alpha
 The purpose of this project is to provide an image of Sabayon spinbase.
 It is just a gentoo stage3 + entropy
 
+## First steps on docker
+
+Ensure to have the daemon started and running:
+
+    sudo systemctl start docker
+
 ## Building docker-sabayon-spinbase
 
     git clone https://github.com/mudler/docker-sabayon-spinbase-amd64.git docker-sabayon-spinbase
     cd docker-sabayon-spinbase
-    docker build -t mudler/docker-sabayon-spinbase .
+    sudo docker build -t mudler/docker-sabayon-spinbase .