Add .pkgdownignore support (#2959) - #2971

Add .pkgdownignore support (#2959)#2971

kyleGrealis wants to merge 2 commits into

r-lib:mainr-lib/pkgdown:mainfrom

kyleGrealis:issue-2959-pkgdownignorekyleGrealis/pkgdown:issue-2959-pkgdownignoreCopy head branch name to clipboard