main: make busybox.conf mode handling less obscure

function                                             old     new   delta
static.mode_mask                                       -      20     +20
main                                                 782     785      +3
static.mode_chars                                     15      13      -2
run_applet_no_and_exit                               450     441      -9
mode_mask                                             24       -     -24
------------------------------------------------------------------------------
(add/remove: 2/2 grow/shrink: 1/2 up/down: 41/-53)            Total: -12 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/Config.in b/Config.in
index 38d8f0c..b65fe45 100644
--- a/Config.in
+++ b/Config.in
@@ -350,7 +350,15 @@
 	  by checking /etc/busybox.conf. (This is sort of a poor man's sudo.)
 	  The format of this file is as follows:
 
-	  <applet> = [Ssx-][Ssx-][x-] (<username>|<uid>).(<groupname>|<gid>)
+	  APPLET = [Ssx-][Ssx-][x-] USER.GROUP
+
+	  s: This user/group are allowed to execute APPLET.
+	     APPLET will run under USER or GROUP.
+	  x: User/group/others are allowed to execute APPLET.
+	     No UID/GID change will be done when it is run.
+	  S: This user/group are NOT allowed to execute APPLET.
+	     APPLET will run under USER or GROUP.
+	  -: User/group/others are not allowed to execute APPLET.
 
 	  An example might help: