Add a note about contributing to the jobs page

[shiroyasha]

Lately, I've been getting quite a few messages from engineers asking if we're hiring. While we're not currently expanding the team, we would definitely give priority to contributors we already know and trust when the time comes.

I propose to add a note on the jobs page with something like:

If you're excited about what we are building, the best way to get involved is by contributing. When opportunities open up, the first place we'll look are those who share our passion and have been part of the project.