changes to release notes

[Jonathan Amsterdam]

Hi Go developers,

Starting with the 1.23 development cycle, release notes will be in markdown, and will be more closely integrated into the development process.

Instead of starting out as a single document, the release notes will consist of a tree of files under doc/next. The tree will be combined into a single file some time after the freeze.

If your CL deserves a release note, it should include a new file in doc/next, or a change to an existing file there. Adding RELNOTE= to the commit message or review comments is no longer supported.

API changes now require new files in doc/next along with the file in api/next. See https://go.googlesource.com/go/+/HEAD/doc/README.md for details. A check for these files will run along with the existing API check.

This is a new process, so we will of course adjust it as needed. We welcome your feedback.

Thanks,

Jonathan