moves intro image to beneath the intro text (apple#25)

Moves the introductory animation/image to beneath a title for the README
and the initial introductory text. Explains what you're seeing a bit
better, while still keeping the image "above the fold" to make it
prominent and encourage people to see and understand what this project
does.

Author: heckj

README.md

@@ -1,4 +1,3 @@
-![introductory movie showing some basic commands](./docs/assets/landing-movie.gif)
 
 # `container`
 
@@ -8,6 +7,8 @@ The application consumes and produces OCI-compliant container images, so you can
 
 `container` uses the [Containerization](https://github.com/apple/containerization) Swift package for low level container, image and process management.
 
+![introductory movie showing some basic commands](./docs/assets/landing-movie.gif)
+
 ## Get started
 
 Install the `container` application on your Mac.