Add entries on download page for 19.1.0 to 19.1.7, 20.1.0 to 20.1.8, and 21.1.0 to 21.1.5#25

nightlark wants to merge 1 commit intollvm:mainllvm/www-releases:mainfrom

nightlark:add-newer-release-download-pagenightlark/llvm-www-releases:add-newer-release-download-pageCopy head branch name to clipboard