Issue template

[jwindhager]

To lower the barrier for newcomers, perhaps we could add a GitHub issue template for walkthroughs? I'm thinking along the lines:

Title:
Walkthrough: ...

Body:

Brief description, perhaps including agenda

Related issues (past iterations, related walkthroughs, ...)

Prerequisites for following along "hands-on" (optional)

Suggested presenters (optional)

...

What do you all think?

[mahesh-panchal]

I'm in favour of this.

[jwindhager]

Created a "draft" PR here: #129