README: add tokei.rs badge
README: add tokei.rs badge

displays a rough estimate of the number of files in the project.
Phizho/tldr,deekim/tldr,UncommonPleb/tldr,slash3b/tldr,slash3b/tldr,Phizho/tldr,felixonmars/tldr,cptdeka10/tldr,cptdeka10/tldr,UncommonPleb/tldr,deekim/tldr,slash3b/tldr,Phizho/tldr,felixonmars/tldr,UncommonPleb/tldr,deekim/tldr,cptdeka10/tldr,felixonmars/tldr