rpy2 not supported on windows

[Peter9192]

Using springtime on windows through the standard installation instructions fails because r-base >= 4.2 is not available for windows (see e.g. conda-forge/r-base-feedstock#248.

Also on rpy2 documentation it says windows is not supported (https://rpy2.github.io/doc/latest/html/overview.html#requirements).

So, we need to make it clear in the docs and/or provide alternative installation instructions.

Alternatively, perhaps we could try to get rid of rpy2 altogheter so we could drop the dependency on r-base>=4.2 (?)