block: Add Kconfig help which notes that ext4 needs CONFIG_LSF

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: Jens Axboe <jens.axboe@oracle.com>
diff --git a/block/Kconfig b/block/Kconfig
index 1ab7c15..e10f4c1 100644
--- a/block/Kconfig
+++ b/block/Kconfig
@@ -64,6 +64,12 @@ config LSF
 	  Say Y here if you want to be able to handle very large files (2TB
 	  and larger), otherwise say N.
 
+	  The ext4 filesystem requires that this feature be enabled in
+	  order to support filesystems that have the huge_file feature
+	  enabled.    Otherwise, it will refuse to mount any filesystems
+	  that use the huge_file feature, which is enabled by default
+	  by mke2fs.ext4.
+
 	  If unsure, say Y.
 
 config BLK_DEV_BSG