More worker build documentation.

Also a small tweak to how to setup venvs to put them somewhere
more obvious.

Change-Id: I140de9aad4e7609edf0d1ab8888e3d224bb3606b
diff --git a/etc/rc.local b/etc/rc.local
new file mode 100644
index 0000000..db2b33a
--- /dev/null
+++ b/etc/rc.local
@@ -0,0 +1,7 @@
+ip netns add nonet
+ip link add veth0 type veth peer name veth1
+ifconfig veth0 172.16.0.1/24 up
+ip link set veth1 netns nonet
+ip netns exec nonet ifconfig veth1 172.16.0.2/24 up
+/sbin/iptables -A INPUT -p tcp --dport 3306 -i eth0 -j DROP
+/sbin/iptables -A INPUT -p tcp --dport 3306 -i eth1 -j DROP