Include the vscode-xml GIF in this repository

The vscode-xml GIF is hosted in the vscode-xml repo. If the file is ever moved/removed from the repository, it will no longer be shown. It would be nice to keep a copy of the new GIF within this repository to prevent this from happening.

This might be a good opportunity to rerecord this GIF if there is anything new in the extension that we want to show off.