[mojosetup] First shot at documentation...

[Ryan C. Gordon]

> Well, if you zip and >> mojosetup to get a self executable thing to distribute, the permissions are maintained without having to do a filter or 
> Setup.File.permission .. if that was not intentional we should make sure it remains that way, because it's handy :)

That's intentional, and definitely won't change...the idea is you can 
probably control the permissions coming out of a .zip (which _can_ store 
Unix permissions) or .tar, but not so much on the physical filesystem 
(since things like iso9660 aren't really good fits with the Unix 
permission model, for example).

Even still, being able to change the permissions in a filter function 
can be useful there in some cases, too.

--ryan.