Update 'Managing Users'

Closing as fixed, but we can reopen if further amendments are needed.

🛬 Merged PR

@AEApple merged a PR to unicode-org/cldr:main

CLDR-18586 Update Managing Users (#4678) https://github.com/unicode-org/cldr/pull/4678 https://github.com/unicode-org/cldr/commit/dd413e9de822f278cb246c42f2d20627306d9b63

Among other things, explain not only how to transfer votes to another vetter, but why it is very important to do that for new vetters. That is, if a vetter starts for locale L, then any votes from previous vetters for L should be copied in — rather than have thousands of abstentions.