docs: Clarify minimum Java version in README (see #1225)

@kwin re. #1225

@cushon merge?

Fixes #1235

COPYBARA_INTEGRATE_REVIEW=#1235 from vorburger:patch-7 38255fa
PiperOrigin-RevId: 741534873

Author: vorburger

README.md

@@ -19,7 +19,8 @@ java -jar /path/to/google-java-format-${GJF_VERSION?}-all-deps.jar <options> [fi
 Note that it uses the `jdk.compiler` module to parse the Java source code. The
 `java` binary version used must therefore be from a JDK (not JRE) with a version
 equal to or newer than the Java language version of the files being formatted.
-An alternative is to use the available GraalVM based native binaries instead.
+The minimum Java version can be found in `core/pom.xml` (currently Java 17). An
+alternative is to use the available GraalVM based native binaries instead.
 
 The formatter can act on whole files, on limited lines (`--lines`), on specific
 offsets (`--offset`), passing through to standard-out (default) or altered