Introduce the concept of metanodes

updates the README file, and makes the post-merge script read the
metanodes file instead of the whole hosts/ directory.

scripts/post-merge

@@ -18,12 +18,12 @@ test -w $TINCCFG || fail "ERR: $TINCCFG is not writeable"
 
 sed -i '/^ConnectTo/d' $TINCCFG
 
-for HOST in hosts/*; do
+while read HOST; do
   # skip hosts without address
-  grep -iq '^Address' -- "$HOST" || continue
+  grep -iq '^Address' -- hosts/"$HOST" || continue
 
-  echo "ConnectTo = ${HOST##*/}" >> $TINCCFG
-done
+  echo "ConnectTo = $HOST" >> $TINCCFG
+done < metanodes
 
 /usr/sbin/invoke-rc.d tinc reload icvpn