RFR: Various cleanups in the JBS section

[Jesper Wilhelmsson]

Moved a table, adding some subsection headlines, and fixed minor bugs.

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Commit messages:
 - Various cleanups in the JBS section

Changes: https://git.openjdk.org/guide/pull/126/files
  Webrev: https://webrevs.openjdk.org/?repo=guide&pr=126&range=00
  Stats: 96 lines in 1 file changed: 33 ins; 22 del; 41 mod
  Patch: https://git.openjdk.org/guide/pull/126.diff
  Fetch: git fetch https://git.openjdk.org/guide.git pull/126/head:pull/126

PR: https://git.openjdk.org/guide/pull/126