create vignette on data quality checks performed by the package

[ernestguevarra]

@AnitaMakori, in this issue for the codeditr package I will be writing a vignette that would describe the different quality checks that the package performs and what these types of errors mean or signify.

I think this information will be useful for either your methods section. I aim to get this completed before next Monday. Once done, I will tag you and feel free to liberally draw from this vignette for your thesis.