m68k: mac: Update Kconfig help

There is still some missing hardware support that affects all models,
such as sound chip and localtalk support. However, many models are well
supported, including the Quadra 800 emulated by QEMU. Missing hardware
support is mostly documented at the web site, so add the URL.

Cc: Joshua Thompson <funaho@jurai.org>
Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Link: https://lore.kernel.org/r/bb327f05f8fb61eeb332cc2ba4e8335570976474.1605847196.git.fthain@telegraphics.com.au
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

arch/m68k/Kconfig.machine

@@ -30,11 +30,9 @@ config MAC
 	select HAVE_ARCH_NVRAM_OPS
 	help
 	  This option enables support for the Apple Macintosh series of
-	  computers (yes, there is experimental support now, at least for part
-	  of the series).
-
-	  Say N unless you're willing to code the remaining necessary support.
-	  ;)
+	  computers. If you plan to use this kernel on a Mac, say Y here and
+	  browse the documentation available at <http://www.mac.linux-m68k.org/>;
+	  otherwise say N.
 
 config APOLLO
 	bool "Apollo support"