[PATCH] clarify menuconfig /(search) help text

Add explicit text about
- where menuconfig '/' (search) searches for strings,
- that substrings are allowed, and
- that regular expressions are supported.

Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>