Have vscode-xml release notes

[xorye]

Whenever there is a new release for vscode-xml, maybe we could make a stripped-down version of the blog post and create release notes, similar to how the https://github.com/microsoft/vscode-java-pack provides release notes with gifs and explanations:

The release notes could appear whenever a new vscode-xml release happens and the user runs the new release for the first time. There could also be a preference that determines whether to automatically show release notes when running future releases for the first time. But, maybe automatically showing the release notes in the first place, might be too obstructive.

There could also be a command to view releases notes, like vscode-java-pack does:

[rgrunber]

I think the issue here is how much time are we able to dedicate to this. Generally we'll create a CHANGELOG entry, which can be viewed from the installed vsix in VS Code, and we do put some effort into ensuring this is understandable for users.

Maybe we could enforce a a rule where for every new feature that happens to be documented in https://github.com/redhat-developer/vscode-xml/tree/master/docs , we take the exact same entry and place it in a page for Release Notes.