added submodules to installation instruction

README

@@ -17,6 +17,9 @@ Pluto:
 ------
     cd <wherever>
     git clone git@git.scc.kit.edu:lo0018/pluto.git
+    for i in server/js/seedrandom server/js/twofish; do
+        (cd $i; git submodule init; git submodule update)
+    done
 
     cd /var/www
     ln -s <wherever>/pluto/server sd