Improve error message when generator not found (yeoman#70)

* Improve error message when generator not found

Closes yeoman/yo#388

* Updates formatting of error message

* Improves error message

Author: mischah

lib/environment.js

@@ -298,10 +298,14 @@ Environment.prototype.create = function create(namespace, options) {
   if (!_.isFunction(Generator)) {
     return this.error(
       new Error(
-        'You don\'t seem to have a generator with the name ' + namespace + ' installed.\n' +
-        chalk.bold('You can see available generators with ' + 'npm search yeoman-generator') +
-        chalk.bold(' and then install them with ' + 'npm install [name]') + '.\n' +
-        'To see the ' + this.namespaces().length + ' registered generators run yo with the `--help` option.'
+        chalk.red('You don\’t seem to have a generator with the name “' + namespace + '” installed.') + '\n' +
+        'But help is on the way:\n\n' +
+        'You can see available generators via ' +
+        chalk.yellow('npm search yeoman-generator') + ' or via ' + chalk.yellow('http://yeoman.io/generators/') + '. \n' +
+        'Install them with ' + chalk.yellow('npm install generator-' + namespace) + '.\n\n' +
+        'To see all your installed generators run ' + chalk.yellow('yo') + ' without any arguments. ' +
+        'Adding the ' + chalk.yellow('--help') + ' option will also show subgenerators. \n\n' +
+        'If ' + chalk.yellow('yo') + ' cannot find the generator, run ' + chalk.yellow('yo doctor') + ' to troubleshoot your system.'
       )
     );
   }