Release Changes on Github/Docs

[claudesortwell]

I understand expo/router is very new and changing fast but it would be great to have releases with a description of what has changed between versions.

I am more than happy to even offer my time to write these if given permission. Please let me know if these already exist and I just haven't looked hard enough.

[EvanBacon]

There's a changelog. We'll move router to expo/expo and it will follow the standard SDK releases.