WIP Add note on ES6
We're modern now at the end of 2022; we finally support the 2015 standard of Javascript!
See https://github.com/civicrm/civicrm-core/pull/24975
I've marked it WIP because I'm never sure how to write docs for things that are yet to be released. I don't even know which version of Civi ES6 is supported from.
Also, not sure if this needs to be separate PRs, but on prog enhancement - do we really promise that front end things will work without Javascript?(!)