Add sidecar example

[PEZ]

Here's a Hello World example for providing manifest-only things from Joyride via a ”Sidecar” extension.

It's quite a lot of boilerplate. But probably a user will keep adding config to the same Sidecar as their library of hacks grows, so most of the boilerplate will only have to be there once. And if we provide it as an example, it shouldn't be much of a bother, especially considering the powers it buys.

I will put some comments in there and also add to the Examples README. We should probably visit the main README about it too.

Do you think Joyride Sidecar is a good name?

We could add some keyboard shortcut and a command to the manifest as well. As those things are the first things you miss when using Joyride up until now.

Please scruitinize the code. I don't want to promote some bad practices. 😄

• [x] I have read the developer documentation.

[borkdude]

Yes, I love the name and it's all looking good to me!