srcmgr needs to own release notes going forward

[markjdb]

• We should strive to keep them up-to-date on an ongoing basis
• Perhaps have a daily/weekly job which mails us when a new Relnotes-tagged commit appears in main or a stable branch.
• We need to maintain a list of highlights for each release

[markjdb]

For 15.0:

• make sure we have some highlights
  • removal of i386?
• make sure we document pkgbase (probably email re@ to see what we need to say)
• ???