be very explicit about docker insert - it does not insert a file into an IMAGE, it creates a new image that adds only that file to its specified parent

docs/sources/commandline/cli.rst

@@ -591,6 +591,12 @@ might not get preserved.
 
     Insert a file from URL in the IMAGE at PATH
 
+Use the specified IMAGE as the parent for a new image which adds a
+:ref:`layer <layer_def>` containing the new file. ``insert`` does not modify 
+the original image, and the new image has the contents of the parent image, 
+plus the new file.
+
+
 Examples
 ~~~~~~~~
 
@@ -600,6 +606,7 @@ Insert file from github
 .. code-block:: bash
 
     $ sudo docker insert 8283e18b24bc https://raw.github.com/metalivedev/django/master/postinstall /tmp/postinstall.sh
+    06fd35556d7b
 
 .. _cli_inspect: