Add a 'hello world' example for posterity

examples/hello-world.factor

@@ -0,0 +1,10 @@
+! This is a bit more complex than the simplest hello world,
+! which is:
+!   "Hello World" print
+! Instead, we define a module, and a main entry hook; when you
+! run the module in the listener with the following command,
+!   "examples/hello-world" run-module
+! It prints the above message.
+
+PROVIDE: examples/hello-world ;
+MAIN: examples/hello-world "Hello World" print ;