update README

README.md

@@ -17,6 +17,15 @@ Liminix, but it may be useful elsewhere too.
 * accept unix datagram socket commands
 * fork a child for each peer socket and run the requested lua script
 
+## how to use it
+
+    $ LUAD_SOCKET_PATH=/var/run/luad/socket luad prelude.lua
+
+    $ LUAD_SOCKET_PATH=/var/run/luad/socket luac script.lua arg1 arg2 ...
+
+The pathname of a Lua script may optionally be passed to luad. It will
+be loaded into the interpreter before it is forked, so whatever it
+does will be available in the children.
 
 ## small print
 
@@ -25,8 +34,3 @@ Liminix, but it may be useful elsewhere too.
 * tested only on Linux. Needs SCM_RIGHTS to send unix file descriptors
   across processes, which seems to be have [implementation quirks on
   different unix flavours](https://gist.github.com/kentonv/bc7592af98c68ba2738f4436920868dc)
-
-
-## TO DO
-
-[.] implement luac