gitattributes: -crlf is not binary

gitattributes: -crlf is not binary

The description of crlf attribute incorrectly said that "-crlf" means
binary.  It is true that for binary files you would want "-crlf", but
that is not the same thing.

We also have supported attribute macros and via that mechanism a handy
"binary" to specify "-crlf -diff" at the same time.  It was not documented
anywhere as far as I can tell, even though the support was there from
the very beginning.

Signed-off-by: Junio C Hamano <redacted>