RFR: Added information on more complex release note options

[calnan]

Included information on how to set up multiple notes for the same issue or linking multiple issues to the same note, and how to set up notes for backports

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Commit messages:
 - Merge remote-tracking branch 'origin/related_releasenote_links' into related_releasenote_links
 - Merge branch 'openjdk:master' into related_releasenote_links
 - removed italics for the link to the Advanced options section
 - updates for typos, formatting changes to address feedback
 - Added information on situations where release notes need to refer to multiple changes, or where multiple release notes are needed for the same change

Changes: https://git.openjdk.org/guide/pull/113/files
 Webrev: https://webrevs.openjdk.org/?repo=guide&pr=113&range=00
  Stats: 16 lines in 1 file changed: 12 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/guide/pull/113.diff
  Fetch: git fetch https://git.openjdk.org/guide.git pull/113/head:pull/113

PR: https://git.openjdk.org/guide/pull/113