autofs: the documentation I wanted to read

This documents autofs from the perspective of what the module actually
supports rather than how automount is expected to use it.

It is formatted using "markdown" and works best with Markdown.pl
(markdown_py doesn't like some constructs).

[rdunlap@infradead.org: copy editing]
Signed-off-by: NeilBrown <neilb@suse.de>
Cc: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Ian Kent <raven@themaw.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>