RFR: Added section on maintainer-pain

[Jesper Wilhelmsson]

Added section on maintainer-pain

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Commit messages:
 - Added section on maintainer-pain

Changes: https://git.openjdk.java.net/guide/pull/37/files
 Webrev: https://webrevs.openjdk.java.net/?repo=guide&pr=37&range=00
  Stats: 20 lines in 1 file changed: 18 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/guide/pull/37.diff
  Fetch: git fetch https://git.openjdk.java.net/guide pull/37/head:pull/37

PR: https://git.openjdk.java.net/guide/pull/37