[renamerOnUpdate] $movie_* elements limitation

[echo6ix]

In Stash a scene can be associated with multiple movies, however renamerOnUpdate will only reference one of those movies. Specifically, it only seems to reference the alphanumerically ascending movie associated with the scene.

This effects

• $movie_scene
• $movie_title
• $movie_year

This may be an edge case, but that still warrants documentation. Consider updating this script's README.md and config files to reflect the limitations. Eg.

NOTES

     $movie_scene, $movie_title, $movie_year
          Elements constrained to referencing one movie per scene. When a scene is associated
          with multiple movies renamerOnUpdate will cite the alphanumerically ascending movie.