media: dev-overlay.rst: cleanup the xvideo example

It makes more sense to place the xvideo example at the body,
keeping the footnote only to justify the design decision.

While this makes the text better, it also fixes the PDF
output.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

Documentation/userspace-api/media/v4l/dev-overlay.rst

@@ -37,6 +37,10 @@ capturing and overlay. Optionally these drivers may also permit
 capturing and overlay with a single file descriptor for compatibility
 with V4L and earlier versions of V4L2. [#f1]_
 
+A common application of two file descriptors is the X11
+:ref:`Xv/V4L <xvideo>` interface driver and a V4L2 application.
+While the X server controls video overlay, the application can take
+advantage of memory mapping and DMA.
 
 Querying Capabilities
 =====================
@@ -289,11 +293,6 @@ To start or stop the frame buffer overlay applications call the
 :ref:`VIDIOC_OVERLAY` ioctl.
 
 .. [#f1]
-   A common application of two file descriptors is the XFree86
-   :ref:`Xv/V4L <xvideo>` interface driver and a V4L2 application.
-   While the X server controls video overlay, the application can take
-   advantage of memory mapping and DMA.
-
    In the opinion of the designers of this API, no driver writer taking
    the efforts to support simultaneous capturing and overlay will
    restrict this ability by requiring a single file descriptor, as in