package/linux-headers: improve help text and prompt

The way the help text and prompt for the kernel header version choice is
written can be misleading to some users.

Rewite them so it is more explicit.

Reported-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/linux-headers/Config.in.host

@@ -8,12 +8,22 @@ choice
 	default BR2_KERNEL_HEADERS_AS_KERNEL if BR2_LINUX_KERNEL
 	default BR2_KERNEL_HEADERS_4_6
 	help
-	  Select the version of kernel header files you wish to use.
-	  You must select the correct set of header files to match
-	  the kernel you intend to use on your target system.
+	  Select the kernel version to get headers from.
+
+	  The kernel headers must be at least as old as the oldest kernel
+	  you intend to run on your target.
+
+	  If you use Buildroot to build a kernel, then you can use
+	  the sources from that kernel as source for the headers.
+
+	  If you choose a custom version of the kernel headers, or choose
+	  to use the same sources as the kernel, you'll have to select
+	  (below) the series of that kernel, so that Buildroot can show
+	  or hide packages that have strong requirements on the kernel
+	  headers.
 
 	config BR2_KERNEL_HEADERS_AS_KERNEL
-		bool "Same as kernel"
+		bool "Same as kernel being built"
 		depends on BR2_LINUX_KERNEL
 
 	config BR2_KERNEL_HEADERS_3_2
@@ -98,7 +108,7 @@ choice
 	depends on BR2_KERNEL_HEADERS_VERSION || BR2_KERNEL_HEADERS_AS_KERNEL
 	default BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_REALLY_OLD
 	help
-	  Set to the kernel headers series you manually set above.
+	  Specify the kernel headers series you manually selected, above.
 
 	  This is used to hide/show some packages that have strict
 	  requirements on the version of kernel headers.