Please add a little complete example, something like

````
  emcc tests/hello_world.cpp -o hello_world.html
  emrun hello_world.html
````

just to make it clear that people don't need to build in any special way. Although reading the test, it looks like people do need to manually include that postjs? Could we perhaps just append it outselves in emrun? Simplest is to add a script element to the html file (or rather a copy of it) right before we run it.