Document "sourcever = 1.5" incompatibility with OpenJDK 9 in README.
diff --git a/README b/README
index ad52fc4..8869996 100644
--- a/README
+++ b/README
@@ -28,6 +28,11 @@
will download a small file named "package-list" from Oracle to
enable linking to the documentation of the standard Java classes.
+ If you are using OpenJDK 9 or later, you will need to edit the
+ "sourcever = 1.5" line in the file "build.properties" before
+ running "ant". Set it to 1.6 or higher. The default value 1.5
+ isn't supported by OpenJDK 9 or later.
+
If you cannot or don't want to use Ant, just compile all .java
files under the "src" directory.
