RFR: 8328627: JShell documentation should be clearer about "remote runtime system"

[Jan Lahoda]

This change attempts to more clearly explain the difference between `-J` and `-R` for JShell.

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Commit messages:
 - 8328627: JShell documentation should be clearer about "remote runtime system"

Changes: https://git.openjdk.org/jdk/pull/18450/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18450&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8328627
  Stats: 17 lines in 2 files changed: 17 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/18450.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18450/head:pull/18450

PR: https://git.openjdk.org/jdk/pull/18450