JOSS review: Remove some documentation from README and add github docs

[kanishkan91]

The author has put together very detailed documentation. Can they consider generating github docs based on the README? All that would be required would be to run the following-

library(pkgdown)
pkgdown::build_site()

The docs can then be linked via a URL similar to this example- https://jgcri.github.io/ambrosia/ (The github repo for this example is here- https://github.com/JGCRI/ambrosia)

OPTIONAL- The README feels heavy. The author can put some of the documentation in a vignette. pkgdown will generate separate pages for different vignettes. I would be happy to describe how this can be implemented. It is quite simple.

openjournals/joss-reviews#5337

[isakro]

I have been wondering about the extent of the README as well. To make the README more succinct, and as it is already repeated in the main vignette, I have therefore removed the example of how to perform and handle multiple dates from the README.

Furthermore, as mentioned in #6, I have also added a second vignette that outlines how the package could be applied in other regions, which also demonstrates some further functionality. Finally, I have also made a pkgdown site hosted with GitHub Pages: isakro.github.io/shoredate/ (which was surprisingly painless to set up).