Document PHP ignore transaction (and other APIs?)

[cschneid]

We have a some php apis we've added that haven't made it into the docs yet.

We should make sure they are clear on usage between both Laravel & Symfony. The code snippet below is how to import the Laravel version of the agent into the file. I don't know what the right code for Symfony is.

Ignore

https://github.com/scoutapp/scout-apm-php/blob/master/src/ScoutApmAgent.php#L60

// At top of file somewhere with other imports
use Scoutapm\Laravel\Facades\ScoutApm;
// Later, when you are in a transaction that you want to ignore
ScoutApm::ignore()