When adding the support for file migration with the file: transport,
we missed adding documentation for it.

Signed-off-by: Fabiano Rosas <farosas@suse.de>
---
 docs/devel/migration.rst | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/docs/devel/migration.rst b/docs/devel/migration.rst
index eeb4fec31f..1488e5b2f9 100644
--- a/docs/devel/migration.rst
+++ b/docs/devel/migration.rst
@@ -41,6 +41,10 @@ over any transport.
 - exec migration: do the migration using the stdin/stdout through a process.
 - fd migration: do the migration using a file descriptor that is
   passed to QEMU.  QEMU doesn't care how this file descriptor is opened.
+- file migration: do the migration using a file that is passed to QEMU
+  by path. A file offset option is supported to allow a management
+  application to add its own metadata to the start of the file without
+  QEMU interference.
 
 In addition, support is included for migration using RDMA, which
 transports the page data using ``RDMA``, where the hardware takes care of
-- 
2.35.3