rand_forest_aorsf included in docs

[bcjaeger]

Hello!

I would like to include the oblique random survival forest in parsnip as an engine for censored regression. I have reviewed the guidelines for contributing engine level documentation and have made .Rmd and .R files for aorsf that mimic existing files for random forest engines, e.g., partykit.

Following the engine-specific guidelines in inst/README-DOCS.md,

1. Use roxygen comments to generate the main .Rd file that R's help system uses.
2. Create an .Rmd file that has the details of the engine.
3. Knit the .Rmd file to .md so the .Rd file from step 1 can link it.
4. Once you are done, run devtools::document() (or use the RStudio IDE) to build the help files.

I had a little trouble on step 3. Knitting my .Rmd file, the error package 'parsnip' required by 'censored' could not be found occurred. So I did not commit the .Rd file. I've tried to figure out what is causing parsnip to be undetected, but haven't figured it out yet.

If you make a PR with a new engine, you can work on the .Rmd file and the tidymodels folks can go through the process of merging it in (but let us know if you want us to do that in the PR).

Since aorsf is a new engine and I am having trouble creating the .Rd file, may I request help getting the documentation files to knit as intended?