add readme for java examples

java/readme.md

+## Compiling and Running Java Demos
+
+To make ("compile") an example, use the included makefile with 
+the name of the java file passed as a variable. For example, to make hello.java:
+
+```bash
+	make NAME="hello"
+```
+
+Then, to run:
+
+```bash
+    java hello 
+```
+
+Or you can compile and run in one step:
+
+```bash
+    make run NAME="hello"
+```
+
+You can also clean temporary `.class` files:
+
+```bash
+    make clean
+```
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