rename.md: add -f flag (#960)
rename.md: add -f flag (#960)

* rename.md: add note about -f flag

* rename.md: add -f example

Phizho/tldr,deekim/tldr,AgamAgarwal/tldr,felixonmars/tldr,Phizho/tldr,felixonmars/tldr,UncommonPleb/tldr,cptdeka10/tldr,zoisom/tldr,UncommonPleb/tldr,cptdeka10/tldr,slash3b/tldr,cptdeka10/tldr,katekyan/tldr,slash3b/tldr,deekim/tldr,UncommonPleb/tldr,zoisom/tldr,AgamAgarwal/tldr,felixonmars/tldr,katekyan/tldr,zoisom/tldr,deekim/tldr,slash3b/tldr,katekyan/tldr,Phizho/tldr