Adding evidence requirements

The video for this tutorial hasn't been produced yet (status: scripted). The script below is what it will show — and Try and Perform work now.

1. 1. Evidence steps

   Photograph, video evidence, measurement, signature and time steps all record proof — not just a tick.

2. 2. In the field

   During a run, an evidence step opens the camera. The step can't be completed until the evidence is attached.