docs: document the Agrona update may need --add-opens (#2566)

Fixes apache/pekko-http#887

Author: raboof

docs/src/main/paradox/release-notes/releases-2.0.md

@@ -16,3 +16,7 @@ by early adopters. This is experimental. This release should not be used in prod
 * Big change for all Java DSL users due to the removal of `pekko.japi.Function` (and related classes) to use `pekko.japi.function.Function` instead (lambdas should recompile ok but if you declared variables or functions explicitly, then you may need to change your imports)
 * New pekko-serialization-jackson3. Users who are happy with the pekko-serialization-jackson, which uses Jackson 2, can stick with that
 * Changed the pekko-serialization-jackson lz4-java dependency to `at.yawk.lz4:lz4-java`, a fork that has important bugfixes
+
+### Upgrade notes
+
+* Agrona was updated from 1.x to 2.x, which [means](https://github.com/aeron-io/agrona/wiki/Change-Log#200-2024-12-17) you may have to add `--add-opens java.base/jdk.internal.misc=ALL-UNNAMED` if you use the Java Module System and Pekko Remote