[MINOR][DOCS] Improve Running R Tests docs

## What changes were proposed in this pull request?

Update Running R Tests dependence packages to:
```bash
R -e "install.packages(c('knitr', 'rmarkdown', 'testthat', 'e1071', 'survival'), repos='http://cran.us.r-project.org')"
```

## How was this patch tested?
manual tests

Author: Yuming Wang <wgyumg@gmail.com>

Closes #18271 from wangyum/building-spark.