fix(new): improve error message when project name does not match regex

Author: beeman

packages/angular-cli/commands/new.ts

@@ -42,6 +42,7 @@ const NewCommand = Command.extend({
       return Promise.reject(new SilentError(oneLine`
         Project name "${packageName}" is not valid. New project names must
         start with a letter, and must contain only alphanumeric characters or dashes.
+        When adding a dash the segment after the dash must start with a letter too.
       `));
     }