RFR: JBS section

[Jesper Wilhelmsson]

Expanding the JBS section with two parts: How to fix an incorrect backport creation, and resolved-incomplete

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Commit messages:
 - How to fix an incorrect backport creation, and resolved-incomplete

Changes: https://git.openjdk.java.net/guide/pull/36/files
 Webrev: https://webrevs.openjdk.java.net/?repo=guide&pr=36&range=00
  Stats: 42 lines in 1 file changed: 41 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/guide/pull/36.diff
  Fetch: git fetch https://git.openjdk.java.net/guide pull/36/head:pull/36

PR: https://git.openjdk.java.net/guide/pull/36