Add gitpod config

[javascripto]

this commit adds support for Gitpod.io, a free automated dev environment that makes contributing and generally working on GitHub projects much easier. It allows anyone to start a ready-to-code dev environment for any branch, issue and pull request with a single click.

[nisarhassan12]

Thanks, @javascripto for the PR.

With your, PRs config in place, Gitpod would do nothing other than cloning the repo. While Gitpod can do a whole bunch of cool stuff that'll help contributors and maintainers greatly.

For instance, try this https://gitpod.io/#https://github.com/mobxjs/mobx/

You'll find out that Gitpod will not only clone the repo but also:

• install all the dependencies.
• run the build task.
• start the docs server.
• run tests in watch mode.
• run the performance benchmarks.

and with pre-builds enabled it installs the dependencies and run the build task ahead of time.

This is how it looks:

[nisarhassan12]

With the changes that I have suggested in place, Gitpod will not only clone the repo but also:

• install the dependencies in src/vue.
• run npm run dev.

Please let me know if you have questions about Gitpod or need any help related to it.