Clarify -x option
Clarify -x option

This also makes it easier to understand what `-x` means (eXclude)
slash3b/tldr,felixonmars/tldr,kuanyui/tldr,deekim/tldr,katekyan/tldr,Phizho/tldr,cptdeka10/tldr,Phizho/tldr,WALL-E/tldr,igorshubovych/tldr,cptdeka10/tldr,katekyan/tldr,deekim/tldr,felixonmars/tldr,zoisom/tldr,UncommonPleb/tldr,UncommonPleb/tldr,cptdeka10/tldr,zoisom/tldr,felixonmars/tldr,AgamAgarwal/tldr,deekim/tldr,katekyan/tldr,AgamAgarwal/tldr,igorshubovych/tldr,slash3b/tldr,Phizho/tldr,UncommonPleb/tldr,zoisom/tldr,slash3b/tldr,WALL-E/tldr,kuanyui/tldr