system: classify init systems

We're going to add more init systems, and some have a very special
purpose, so we do not want to mix them with the mundane platitude of
existing init systems.

Add comments to separate the two.

Note that the list would already contain comments, when a br2-external
tree provides an init system, so those new comments would not be totally
weird-looking.

Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Cc: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Reviewed-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>

system/Config.in

@@ -87,6 +87,8 @@ choice
 	prompt "Init system"
 	default BR2_INIT_BUSYBOX
 
+comment "General purpose"
+
 config BR2_INIT_BUSYBOX
 	bool "BusyBox"
 	select BR2_PACKAGE_BUSYBOX
@@ -145,6 +147,8 @@ comment "systemd highly recommends Linux >= 4.15"
 	depends on BR2_INIT_SYSTEMD
 	depends on !BR2_TOOLCHAIN_HEADERS_AT_LEAST_4_15
 
+comment "Special purpose (read help)"
+
 config BR2_INIT_NONE
 	bool "Custom (none)"
 	select BR2_PACKAGE_SKELETON_INIT_NONE if BR2_ROOTFS_SKELETON_DEFAULT