Updated docs, moved lua into its own thread

doc/lua_api.md

@@ -1,5 +1,9 @@
 # Overview
 
+> :warning: 
+> Not all of this is presently implemented. See the [README](../README.md) for details
+> on implementation status.
+
 The lua script must have the following form:
 
 ```lua
@@ -99,4 +103,24 @@ You can test the version using either `.version`, which returns either 4 or 6, o
 `.is_v4` and `.is_v6`. If you need the IPv6-mapped version of a v4 address, (i.e., 
 `::ffff:0.0.0.0`), this is available through `.to_v6` 
 
-This is probably most useful in conjunction with `stftpd.Cidr`
+This is probably most useful in conjunction with `stftpd.Cidr`
+
+# Examples
+
+Probably the most useful starting point for your own script will be the following:
+
+```lua
+return function(path, client, size)
+  if path:match("^/?^/?https?://") then
+    if path:sub(1,1) == "/" then
+      path = path:sub(2)
+    end
+    return resource.HTTP(path)
+  end
+  return resource.FILE(path)
+end
+```
+
+This detects HTTP (or HTTPS) urls, and transparently proxies them to the appropriate HTTP server. 
+Some TFTP clients automatically insert a leading `/`, so this function strips it if given.
+If the given path doesn't look like an HTTP URL, this example tries to handle it as a file.