add another note about executable scripts

DEVEL/Developer.txt

@@ -104,6 +104,7 @@ keep reading.  Otherwise, you are done with this section.
 		PRE	(run your code before the NetHack hook)
 		POST	(run your code after the NetHack hook)
 	and HOOKNAME is the normal git name of the hook.
+   Make sure the hooks are executable (chmod +x ...).
    Be sure to test carefully since the composition of two bits of code may or
    may not do what you want.
 2) to install other bits on setup: