RFR: 8333230: Improve code example in doclet package

[Nizar Benalla]

Can I please get a review for this simple change? It's an attempt to improve the code example in doclet package.
Here are the generated docs with the [new code example.](https://cr.openjdk.org/~nbenalla/GeneratedDocs/newDocletExample/api/jdk.javadoc/jdk/javadoc/doclet/package-summary.html#Example.java)

I tried to go for simplicity while showing some features of the standard doclet, running this Doclet on a small project gives the following ouput.


Note: org.example.Example -> src/main/java/org/example/Example.java CLASS
Note: org.example.SimpleDoclet -> src/main/java/org/example/SimpleDoclet.java CLASS



TIA

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Commit messages:
 - Update Doclet code example

Changes: https://git.openjdk.org/jdk/pull/20619/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20619&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8333230
  Stats: 112 lines in 1 file changed: 35 ins; 44 del; 33 mod
  Patch: https://git.openjdk.org/jdk/pull/20619.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20619/head:pull/20619

PR: https://git.openjdk.org/jdk/pull/20619