Add Java 9 compatibility section

Author: sormuras

documentation/src/docs/asciidoc/release-notes-5.0.0-M6.adoc

@@ -14,6 +14,37 @@ For a complete list of all _closed_ issues and pull requests for this release, c
 link:{junit5-repo}+/milestone/11?closed=1+[5.0 M6] milestone page in the JUnit repository
 on GitHub.
 
+==== Java 9 compatibility
+
+The main target of JUnit is Java 8. Therefore, it won't ship with compiled module
+descriptors. However, since <<release-notes-5.0.0-m5,milestone M5>> each artifact
+published by JUnit 5 ships with a stable automatic module name declared in the
+JAR manifest. That allows test module authors to require well-known JUnit module
+names, like:
+
+```
+module foo.bar {
+  requires org.junit.jupiter.api;
+}
+```
+
+Usually it's sufficient to run tests on the class-path. There's no change between
+Java 8 and 9. All command line based tools and IDEs continue to work with JUnit 5
+_out-of-the-box_ -- if they support the JUnit Platform. If your tool of choice
+does not support JUnit 5 yet, you may always resort to the `ConsoleLauncher` or
+even to the executable `junit-platform-console-standalone` all-in-one jar.
+
+Running JUnit Jupiter tests on the module path is implemented by *pro*, a Java 9
+compatible build tool. It's available at https://github.com/forax/pro
+
+*pro* supports black-box and white-box testing. The former is used by module
+surface tests that only access the exported bits of the application modules.
+The latter is using a module descriptor merge-technique allowing access to
+`protected` and package-private types as well as not exported packages.
+
+See https://github.com/forax/pro/tree/master/src/test/java for test module
+examples: `integration.pro` is a black-box module, `com.github.forax.pro.api`
+and `com.github.forax.pro.helper` are white-box test modules.
 
 [[release-notes-5.0.0-m6-junit-platform]]
 ==== JUnit Platform