add docs for exit setup

docs/exit-setup.md

@@ -0,0 +1,12 @@
+
+to configure lokinet to be an exit add into `lokinet.ini` `[network]` section the following:
+
+    exit=true
+    keyfile=/var/lib/lokinet/exit.private
+    reachable=1
+    ifaddr=10.0.0.1/16
+
+post setup for exit (as root) given `eth0` is used to get to the internet:
+
+    # echo 1 > /proc/sys/net/ipv4/ip_forward
+    # iptables -t nat -A POSTROUTING -s 10.0.0.0/16 -o eth0 -j MASQUERADE