Documenting HTRfit install
Explain what to do in case you get the following error message when trying to install HTRfit:
Warning messages: 1: In install.packages(...) : installation of package ‘XML’ had non-zero exit status 2: In install.packages(...) : installation of package ‘gridSVG’ had non-zero exit status 3: In install.packages(...) : installation of package ‘plotROC’ had non-zero exit status