README "how to update dependencies"

Currently:

### How to update dependencies from nuget?
-   `git submodule update --init --recursive` to install all submodules
-   Make sure you have [ruby](https://www.ruby-lang.org/de/downloads/)
    install and that it is available in your path
-   Run `rake postclean` or simply double click on `postclean.bat`. This
    will update all nuget packages and copy the dependencies in the
    package `inst/lib` folder.

Update to describe the current workflow (using update_core_files.R?).

Open-Systems-Pharmacology / OSPSuite-R

README "how to update dependencies" #1452