docs: note about select in kconfig-language.txt

A warning note from Sam Ravnborg about kconfig's select evilness,
dependencies and the future (slightly corrected).

Signed-off-by: Jarek Poplawski <[e-mail]>
Cc: Sam Ravnborg <[e-mail]>
Cc: Roman Zippel <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

Documentation/kbuild/kconfig-language.txt

···
   times, the limit is set to the largest selection.
   Reverse dependencies can only be used with boolean or tristate
   symbols.
+  Note:
+	select is evil.... select will by brute force set a symbol
+	equal to 'y' without visiting the dependencies. So abusing
+	select you are able to select a symbol FOO even if FOO depends
+	on BAR that is not set. In general use select only for
+	non-visible symbols (no promts anywhere) and for symbols with
+	no dependencies. That will limit the usefulness but on the
+	other hand avoid the illegal configurations all over. kconfig
+	should one day warn about such things.
 
 - numerical ranges: "range" <symbol> <symbol> ["if" <expr>]
   This allows to limit the range of possible input values for int