Create vignette for readQFeatures() and co

[cvanderaa]

We could have a vignette devoted to reading data with readQFeatures. It would provide a bit more details on how the function works and also provides concrete examples for the different use case. For instance, we could explicitly show how to read LFQ vs labelled data, PSM vs peptide/protein data. This vignette would show how flexible and easy reading data is for any proteomics dataset. It would also serve as a useful reference everytime someones ask "can I use it for reading [name of software/technology] data?", see for example this issue: UCLouvain-CBIO/scp#48.

I think the readSCP vignette could provide us with a head start: https://uclouvain-cbio.github.io/scp/articles/read_scp.html