add empty library directory

testing/get-renv.sh

@@ -1,2 +1,9 @@
 #!/usr/bin/env bash
 sudo apt install r-base
+# create empty folder for user library.
+# necessary for non-root users who have
+# never installed an R package before.
+# Alternatively, we require the renv
+# package to be installed already, then we can
+# omit that.
+Rscript -e 'dir.create(Sys.getenv("R_LIBS_USER"))'