Augment template

[amueller]

I think we should augment the template to start with a motivation and an example of what the solution will look like to users.

[adrinjalali]

I think we (I at least) should start using that template, instead of taking another SLEP as a starting point :D

[NicolasHug]

yeah, the current template addresses these points it seems:

It should describe the
existing problem that it is trying to solve and why this SLEP makes the
situation better. It should include examples of how the new functionality
would be used and perhaps some use cases

[amueller]

I think motivation should be a separate section.