This sets up R + RStudio + IRKernel for a repository that contains:
1. A `runtime.txt` file with the text:
r-<year>-<month>-<date>
Where 'year', 'month' and 'date' refer to a specific
date snapshot of https://mran.microsoft.com/timemachine
from which libraries are to be installed.
2. An optional `install.R` file that will be executed at build time,
and can be used for installing packages from both MRAN and GitHub.
It currently sets up R from the ubuntu repository being used. This
is unideal, and we should investigate other solutions!
Fixes#24
yuvipanda