feat: add documentation page

- fix rmarkdown dependency issue

Refs #23
1 job for master in 2 minutes and 32 seconds (queued for 1 second)
Status Name Job ID Coverage
failed deploy #168114


Name Stage Failure
deploy Test
Calls: <Anonymous> -> setwd -> dirname -> abs_path
In addition: Warning message:
In normalizePath(path, winslash = winslash, mustWork = mustWork) :
path[1]="inst/app/www/documentation/documentation.Rmd": No such file or directory
Execution halted
The command '/bin/sh -c R -e 'rmarkdown::render("inst/app/www/documentation/documentation.Rmd")'' returned a non-zero code: 1
Connection to closed.
Cleaning up file based variables
ERROR: Job failed: exit code 1