[13u-communication] End of maintenance & invitation for new maintainers

[Rob McKenna]

I'm sending this mail to notify the community that the current maintainers
intend to step down as maintainers for the JDK 13 Updates forest [1] at the
end of March, or sooner, if new maintainers were to step up. [2]

This being the case we would like to invite prospective new maintainers to
step forward at this point to ensure a smooth transition should they wish to
maintain this forest beyond the end of March.

      -Rob

[1] https://hg.openjdk.java.net/jdk-updates/jdk13u
[2] https://openjdk.java.net/projects/jdk-updates/maintainers.html