Add guidelines for merge request logs.
Add guidelines for merge request logs.

We need more information from developers for new merge requests. This
adds guidelines that we can point them to, if needed.

keithroe/vtkoptix,keithroe/vtkoptix,keithroe/vtkoptix,keithroe/vtkoptix,keithroe/vtkoptix,keithroe/vtkoptix,keithroe/vtkoptix,keithroe/vtkoptix