dax: replace XIP documentation with DAX documentation

Based on the original XIP documentation, this documents the current state
of affairs, and includes instructions on how users can enable DAX if their
devices and kernel support it.

Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Andreas Dilger <andreas.dilger@intel.com>
Cc: Boaz Harrosh <boaz@plexistor.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/Documentation/filesystems/00-INDEX b/Documentation/filesystems/00-INDEX
index ac28149..9922939 100644
--- a/Documentation/filesystems/00-INDEX
+++ b/Documentation/filesystems/00-INDEX
@@ -34,6 +34,9 @@
 	- directory containing configfs documentation and example code.
 cramfs.txt
 	- info on the cram filesystem for small storage (ROMs etc).
+dax.txt
+	- info on avoiding the page cache for files stored on CPU-addressable
+	  storage devices.
 debugfs.txt
 	- info on the debugfs filesystem.
 devpts.txt
@@ -154,5 +157,3 @@
 	- info on XFS Self Describing Metadata.
 xfs.txt
 	- info and mount options for the XFS filesystem.
-xip.txt
-	- info on execute-in-place for file mappings.