CodingGuidelines: update 'rough' rule count

Changed inaccurate count of "rough rules" from three to the more
generic 'a few'.

Signed-off-by: Julian Gindi <juliangindi@gmail.com>
Reviewed-by: Eric Sunshine <sunshine@sunshineco.com>
Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/CodingGuidelines

@@ -1,5 +1,5 @@
 Like other projects, we also have some guidelines to keep to the
-code.  For Git in general, three rough rules are:
+code.  For Git in general, a few rough rules are:
 
  - Most importantly, we never say "It's in POSIX; we'll happily
    ignore your needs should your system not conform to it."