Please help with the Go 1.21 release notes

[Brandon Kessler]

Hi Gophers,

We appreciate the hard work everyone has put into the Go 1.21 release. In addition to writing Go code, we need to communicate notable changes to all the future Go 1.21 users so that our hard work doesn't go unseen. 

There are currently multiple TODOs at https://tip.golang.org/doc/go1.21. We need everyone's help with summarizing the improvements by completing the Go 1.21 release notes draft. Doing so will unblock the Go 1.21 release. 

You can review existing CLs for the Go 1.21 release notes at https://go-review.googlesource.com/q/file:doc/go1.21.html+status:open. 

Please pick some improvement that you feel comfortable explaining and take ownership over its resolution. Thank you again for your contributions, we really appreciate your help!

Brandon for the Go Team