Improve validation message "Path can contain only ..." for project names

During creation of a project with the planned name usaußenpolitik I got the validation error message Path can contain only letters, digits, '_', '-' and '.'. Cannot start with '-', end in '.git' or end in '.atom' which allows me guess that the umlaut ß is probably not supported, but it'd be nice if the error message would contain the specific constraints since ß is technically a letter - and even if by some definition it's not I as a user might not know that and ideally I shouldn't have to think when it's not necessary.