Document karma's :runner-ns option

[simonacca]

Spent some time figuring out how to perform custom initialization steps before test execution in karma, thought it might be useful to others

[thheller]

Due to engine limitations your example has some issues. The only real way to do this is copying the whole shadow.test.karma namespace and adding what you need, just calling into that ns does not work reliably.

I've been meaning to address this limitation, but haven't found a proper solution yet.