.Renviron support

Thanks for the awesome script, it really is useful.
Would it be possible to add a tiny support for R ?
There just needs to be an `.Renviron` file to be created in `~/` with `http_proxy=proxy` and `https_proxy=proxy` lines.

Start by locating the repository entry point that configures proxy settings and inspect how it persists settings for supported environments. Add the requested .Renviron behavior for R, creating it under the user's home directory with the specified proxy variables; done means the generated file contains both lines and existing proxy configuration still works.

Written by the indexing model from the issue text.