RFR: 7903866: Add an example

[Andrew Haley]

It's an example, for example. We need more.

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Commit messages:
 - Add an example

Changes: https://git.openjdk.org/apidiff/pull/26/files
  Webrev: https://webrevs.openjdk.org/?repo=apidiff&pr=26&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903866
  Stats: 15 lines in 1 file changed: 15 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/apidiff/pull/26.diff
  Fetch: git fetch https://git.openjdk.org/apidiff.git pull/26/head:pull/26

PR: https://git.openjdk.org/apidiff/pull/26