linux: mention 3.x.y kernels in 'custom version' help

(also fix grammatical error versions -> version)

Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

linux/Config.in

@@ -37,8 +37,8 @@ config BR2_LINUX_KERNEL_SAME_AS_HEADERS
 config BR2_LINUX_KERNEL_CUSTOM_VERSION
 	bool "Custom version"
 	help
-	  This option allows to use a specific 2.6.x or 2.6.x.y
-	  official versions, as available on kernel.org
+	  This option allows to use a specific official version from
+	  kernel.org, like 2.6.x, 2.6.x.y, 3.x.y, ...
 
 config BR2_LINUX_KERNEL_CUSTOM_TARBALL
 	bool "Custom tarball"