RFR: 8356420: Provide examples on wrapping System.in

[Naoto Sato]

With the introduction of `stdin.encoding` ([JDK-8350703](https://bugs.openjdk.org/browse/JDK-8350703)), some guidance for users to decode `System.in` would be desirable. Adding examples in the field description would help.

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Commit messages:
 - initial commit

Changes: https://git.openjdk.org/jdk/pull/25155/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25155&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8356420
  Stats: 29 lines in 3 files changed: 21 ins; 0 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/25155.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25155/head:pull/25155

PR: https://git.openjdk.org/jdk/pull/25155