Add a page with links to other (general) R resources

[katherinehebert]

We could create a general resource page with links to pages like https://github.com/iamericfletcher/awesome-r-learning-resources, https://www.rfordatasci.com/, and https://ourcodingclub.github.io/, etc. and other available resources and workshops that are relevant for people looking to learn R. We have resources per workshop in the books and slides, but a list of very general resources as a starting point would be helpful.