Documentation: Add links to Colab into Rmd and README file

Users are not able to use R library as effectively as Python because documentation is incomplete.

from Discord (28 Oct 2024):


We can't just directly edit the README since it's generated from Rmd

There is a lot of info in the [Python README](https://github.com/harmonydata/harmony/edit/main/README.md) which needs to be copied over:

* R markdown notebook
* Colab notebook
* Links to tutorials

but we can't just copy and paste, you need to copy just the information that is relevant for R, adapting where necessary. Then ideally update the Rmd, run the process to generate the README, and update CRAN if possible.