Add comments about disabled tests and JVM args

arrow/build.gradle.kts

@@ -37,7 +37,11 @@ dependencies {
 plugins.withType<JavaPlugin> {
     tasks {
         configureEach<Test> {
+            // Tests disabled on Windows due to failures. Arrow is not tested on Windows:
+            // https://arrow.apache.org/docs/java/install.html#system-compatibility
             enabled = !OperatingSystem.current().isWindows
+            // The following JVM options are required when using certain JDKs >= 9
+            // https://arrow.apache.org/docs/java/install.html#java-compatibility
             jvmArgs("-XX:+IgnoreUnrecognizedVMOptions")
             jvmArgs("--add-opens=java.base/java.nio=ALL-UNNAMED")
         }