[jdk17u-dev] RFR: 8272558: IR Test Framework README misses some flags

[Aleksey Shipilev]

This is a simple docs amendment. Without it, IR Framework backports are not clean and require tedious resolves.

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Commit messages:
 - Backport 5189047d09e976cfd17d4ab5ec12097c242f3435

Changes: https://git.openjdk.org/jdk17u-dev/pull/2795/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=2795&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8272558
  Stats: 17 lines in 1 file changed: 2 ins; 0 del; 15 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/2795.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/2795/head:pull/2795

PR: https://git.openjdk.org/jdk17u-dev/pull/2795