add pkgdown

[nmontalbanocouncil]

PRs (e.g. #28) failed at Build site sections with the following error:

-- Building articles -----------------------------------------------------------
Writing 'articles/index.html'
Reading 'vignettes/councilverse.Rmd'
-- RMarkdown error -------------------------------------------------------------

Quitting from lines 29-33 [unnamed-chunk-3] (councilverse.Rmd)

Error in map():
ℹ In index: 1.
Caused by error in render_rmarkdown():
! Failed to render RMarkdown
Caused by error:
! in callr subprocess.
Caused by error:
! there is no package called 'tidyverse'
Backtrace:
▆

1. └─base::library(tidyverse)
   Execution halted
   Error: Process completed with exit code 1.