RFR: Smaller fixes and clarifications

[Jesper Wilhelmsson]

Fixed a link
Split a line to make the second half more prominent
Added info on how to deal with additional versions for a release note

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Commit messages:
 - Added info on release notes
 - Minor fixes

Changes: https://git.openjdk.org/guide/pull/163/files
  Webrev: https://webrevs.openjdk.org/?repo=guide&pr=163&range=00
  Stats: 4 lines in 3 files changed: 2 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/guide/pull/163.diff
  Fetch: git fetch https://git.openjdk.org/guide.git pull/163/head:pull/163

PR: https://git.openjdk.org/guide/pull/163