`r_beginners`: some more possible updates

[hansvancalster]

During review of @pietervsd ' PR #247 I noticed a few other places where an update might be needed:

• dplyr::gather and dplyr::spread should be replaced by dplyr::pivot_longer and dplyr::pivot_wider
• the section on connection to inbo databases could be improved by making use of the inbodb package (@ElsLommelen )

[ElsLommelen]

And another important thing that certainly needs an update for r_beginners (and also for other users): in the documentation of the R and RStudio installation, the installation path of R is changed to C:\R\R.x.y.z, while IT still installs R in the program files folder. Today I helped someone encountering problems with it for the second time in two weeks... No matter which choice is made, but the IT installation and the documentations should correspond.

And see also #149.