README: add maven prerequisite
diff --git a/README.md b/README.md
index 1e70f9d..98ec28e 100644
--- a/README.md
+++ b/README.md
@@ -31,6 +31,8 @@
 itself. We do ask you to install it and use it before submitting pull requests,
 though.
 
+Running the Java unit tests requires Maven 3: `sudo apt-get install maven`.
+
 Usage
 =====