RFR: 8357000: Write overview documentation for start of release changes [v2]

[Joe Darcy]

> First attempt to populate "supplementary docs" with a discussion of the start of release changes. For reference on the idea of supplementary docs, see the thread
> 
> "Where to put supplementary docs?"
> https://mail.openjdk.org/pipermail/jdk-dev/2025-April/009975.html

Joe Darcy has updated the pull request incrementally with one additional commit since the last revision:

  Respond to review feedback.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/25317/files
  - new: https://git.openjdk.org/jdk/pull/25317/files/75130c26..8e10f57b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25317&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25317&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/25317.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25317/head:pull/25317

PR: https://git.openjdk.org/jdk/pull/25317