create vignette named mwana.Rmd or mwana.qmd

[ernestguevarra]

A vignette with the same name as the package gets its own tab in the package website using pkgdown. This is generated as the Getting Started tab on the menu of the package website.

I think this is nice to have as this can be more expository with regard to how the full workflow runs and can then refer to the other vignettes for the details on each step.