MAINT: Migration notice and link to new JAX site

[mmcky]

This PR

• [x] notifies of a new lecture series and location for lecture
• [x] provides a link

Things to do:

• [x] merge once jax.quantecon.org is officially live
• [ ] review style with @jstac for building a standard QuantEcon admonition for new lecture location notification.

[github-actions[bot]]

🚀 Deployed on https://6465f82e04fb5110134a05b0--epic-agnesi-957267.netlify.app

[mmcky]

@jstac what do you think about this?

Maybe change New website to Moved lecture

[jstac]

Thanks @mmcky