kconfig-language: elaborate on the type of a choice

The type of a choice can be specified explicitely or it will be
set according to members of the choice group, see menu.c:menu_finalize().
Signed-off-by: Dirk Gouders <dirk@gouders.net>
Signed-off-by: Michal Marek <mmarek@suse.com>

Documentation/kbuild/kconfig-language.txt

@@ -284,12 +284,17 @@ choices:
 	"endchoice"
 
 This defines a choice group and accepts any of the above attributes as
-options. A choice can only be of type bool or tristate, while a boolean
-choice only allows a single config entry to be selected, a tristate
-choice also allows any number of config entries to be set to 'm'. This
-can be used if multiple drivers for a single hardware exists and only a
-single driver can be compiled/loaded into the kernel, but all drivers
-can be compiled as modules.
+options. A choice can only be of type bool or tristate.  If no type is
+specified for a choice, it's type will be determined by the type of
+the first choice element in the group or remain unknown if none of the
+choice elements have a type specified, as well.
+
+While a boolean choice only allows a single config entry to be
+selected, a tristate choice also allows any number of config entries
+to be set to 'm'. This can be used if multiple drivers for a single
+hardware exists and only a single driver can be compiled/loaded into
+the kernel, but all drivers can be compiled as modules.
+
 A choice accepts another option "optional", which allows to set the
 choice to 'n' and no entry needs to be selected.
 If no [symbol] is associated with a choice, then you can not have multiple