Is your feature request related to a problem? Please describe.
Contributors should be aware of the style typically used by R Core, so that R Core can focus on the code and not style issues when reviewing patches. Questions about style have come up on the Slack and I have also given feedback about this when reviewing patches before submission to Bugzilla.

Describe the solution you'd like
A new chapter/section on style. There is a little about R coding standards in the R-internals manual, e.g. using an indentation of 4 spaces in R and C code. Other style points I'm not sure are documented anywhere but I think are generally followed:

• spaces after commas and either side of operators
• <- rather than = for assignment
• " rather than ' for quoting text
• TRUE and FALSE not T and F
• lines no longer than 80 characters

We could work through https://style.tidyverse.org/ to check what is common to base R. @mmaechler has also given talks about style and may know if there is another reference we should use.

Describe alternatives you've considered
N/A

Additional context
N/A