additional gitpod config

[GitMensch]

It always slows down if one needs to prepare things for a quick pull request.
This is where gitpod.io comes in, which allows to create a build environment with a single click.

I'd like to contribute a gitpod configuration (x11, possibly sdl, maybe wincon if that works with wine easily and definitely vt if that gets in), allowing it to work "out of the box".

This would mean adding a single .gitpod.yml file, if that's something that has a high chance to be pulled in, either with or without a "code on GitPod" entry in the main README and/or docs/README.md.

As I'd like to know before doing that work... @wmcbrine @Bill-Gray What do you think of that?

After this is contributed, the following may be done from the project site:

• login and install the app here, see https://github.com/apps/gitpod-io
• configuring pre-builds

but as noted, that's "optional";

Some benefits of GitPod:
nice performance, running without costs, full coding and building and testing possible in the browser from anywhere, when pre-builds are active the development can start nearly in an instant, in theory also easy for people to start coding on the project
GitPod is similar to GH code workspaces, but for open source contributions free of charge - and exists since years, while GH workspaces are relatively new