Simplify list of prerequisites for Ubuntu and Fedora

[llrs]

I added the command to find the list of prerequisites for Ubuntu and Fedora and also how to install them without installing R via the OS package manager.

The instructions for Windows and Linux match.

• In linux there the configuration is done via "$TOP_SRCDIR/configure" --enable-R-shlib but in windows it doesn't seem to be needed.
• Both instructions end with make check and the optional make check-devel and make check recommended. It was commented to use make check-all but this might take too long.
• The guide assumes that there is no previous attempt and the users starts from a clean state. But it might be nice to mention something about how to make sure it is a clean build.
• In windows I do not make any mention to Rstudio, perhaps I can add a mention that users should go and select which version of R want to use? (While for Linux users I could mention the RSTUIDO_WHICH_R variable to control that)

Currently the macOS section is empty, there is not even a "In progress" note. Should I document that?

Let me know if I missed some other comments from the meeting, @hturner.

[hturner]

Thanks @llrs. This PR addresses the issue of prerequisites. In response to other issues:

• We use --enable-R-shlib on Linux to allow use of the built R-devel with RStudio. This is not needed on Windows.
• Yes, I think we can leave make check-all out for now. All these additional checks are more relevant for testing patches and perhaps we should document more in the relevant section.
• Remaining points: I will break these out as outstanding issues for you/someone else to pick up later.