Create a contributor guide

[SHAESEN2]

Idea

What is your idea for a new plot/table?

Do you have any examples you can share of what it looks like?

What potential packages/functions could be used to make this plot?

Are you interested to implement this yourself?

[SHAESEN2]

Updating the wiki might be easier.

[ddsjoberg]

Update with details

• tibbles vs data.frames
• use of $ internally
• details on the unit testing framework that has been implemented (sometimes when I do a full check of the package, the entire test file is deleted and re-saved with some changes to the header, I think). As this is a non-standard workflow, details for contributors would be incredibly useful
• add details for expectations of testing for new PRs. the package has amazing testing coverage, but as a new contributor is was difficult to orient myself on how to integrate my own unit tests

[SHAESEN2]

Updated Wiki.

[cschaerfe]

Updated https://github.com/openpharma/visR/wiki/Contribute with link to https://github.com/openpharma/visR/wiki/Coding-principles