Add badge to Readme showing the status of the "next" build

[JonasHelming]

If the build on main fails, it is likely that the underlying Theia project has some API breakage. We should notify interested parties, either some committer or a mailing list in this case. @vince-fugnitto @marcdumais-work Any thoughts on this?

see also #122 introducing a build against "next"

[vince-fugnitto]

@JonasHelming I think the mailing list would be too noisy if we start sending emails when the build fails, perhaps whoever is interested can turn on their settings for failed builds? The only issue is that it might not be granular to which repo they want notifications for:

We could also add a badge in the main-repo's readme (similarly to vscode-builtin-extensions) to display the build status of the generator.

[JonasHelming]

@vince-fugnitto Do you get notifications on this repo? If so, if it is at least you and me, I believe we are good already.

[vince-fugnitto]

@vince-fugnitto Do you get notifications on this repo? If so, if it is at least you and me, I believe we are good already.

@JonasHelming I believe so, and I agree that it's likely enough, we would not want to add noise to the mailing list about failed builds in the generator 👍

[JonasHelming]

OK let us wait until the tree editor is fixed then

[JonasHelming]

Depending on the outcome of the discussion here: eclipse-theia/theia-ide#186
We also might want to add the badge to the Theia repo