adding a few things to show how to compile and run

1. added build.xml
2. added compile
3. added run
4. Main.java has less threads. On my machine too much resource
   usage was causing a 701 error.

To use this example, run the following commands
$ cd Rootbeer_primeNumbers
$ ./compile
$ ./run
Merge pull request #1 from pcpratts/master

adding a few things to show how to compile and run