How to run entry point scripts

At this time there's only 1 addon that has tests, and that is Selenium IDE.
To be able to run this you also need to pass in `--with-untrusted` as an argument. Might as well add this in the docs.

Given that `functional` tests are the most important, I'd actually change this example to run the functional testrun. So use `testrun_fucntional` instead of `testrun_addons`