Add a "tour" to new user creation.

[Morgul]

We should have some onboarding to help explain to users how to use RPGKeeper. A 'tour' library (like https://pulsardev.github.io/vue-tour/) is probably best for this.

Full details to be fleshed out later.

[PiotrZakrzewski]

Or a screencast YouTube video. Easier to make.