f2fs: update f2fs Documentation

This patch describes the inline_data support in f2fs document.
Signed-off-by: Huajun Li <huajun.li@intel.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

Documentation/filesystems/f2fs.txt

@@ -120,6 +120,8 @@ active_logs=%u         Support configuring the number of active logs. In the
 disable_ext_identify   Disable the extension list configured by mkfs, so f2fs
                        does not aware of cold files such as media files.
 inline_xattr           Enable the inline xattrs feature.
+inline_data            Enable the inline data feature: New created small(<~3.4k)
+                       files can be written into inode block.
 
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