btrfs-progs: docs: add FS_IOC_READ_VERITY_METADATA support

As of bfcf6d04f8ee ("btrfs: handle FS_IOC_READ_VERITY_METADATA ioctl")
the kernel supports FS_IOC_READ_VERITY_METADATA for btrfs (6.14).  Add
that to the docs.

Pull-request: #970
Signed-off-by: Allison Karlitskaya <allison.karlitskaya@redhat.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: allisonkarlitskaya

Documentation/Interoperability.rst

@@ -28,6 +28,7 @@ The ioctls supported by btrfs:
 
 * `FS_IOC_ENABLE_VERITY <https://www.kernel.org/doc/html/latest/filesystems/fsverity.html#fs-ioc-enable-verity>`__
 * `FS_IOC_MEASURE_VERITY <https://www.kernel.org/doc/html/latest/filesystems/fsverity.html#fs-ioc-measure-verity>`__
+* `FS_IOC_READ_VERITY_METADATA <https://www.kernel.org/doc/html/latest/filesystems/fsverity.html#fs-ioc-read-verity-metadata>`__
 
 See also:
 https://www.kernel.org/doc/html/latest/filesystems/fsverity.html