media: docs: selection: rename files to something meaningful

These files have an automatically-generated numbering. Rename them
with a name that suggests their meaning.
Reported-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

Documentation/media/uapi/v4l/selection-api.rst

@@ -9,8 +9,8 @@ Cropping, composing and scaling -- the SELECTION API
 .. toctree::
     :maxdepth: 1
 
-    selection-api-002
-    selection-api-003
-    selection-api-004
-    selection-api-005
-    selection-api-006
+    selection-api-intro.rst
+    selection-api-targets.rst
+    selection-api-configuration.rst
+    selection-api-vs-crop-api.rst
+    selection-api-examples.rst