Add mkdocs and change menu names to avoid margin collisions (#468)

docs/guides/first-steps.md

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+First steps to use Yii2-usuario
+===============================
+
+After installing the extension and having configured everything, you need setup your application with the all the user related stuff, e.g.
+
+* creating first users, roles, permissions, ...
+* assigning permissions and roles to users
+* extending your controllers with access restrictions  
+* starting user management
+
+## Creating your first user
+
+There are several ways to do that:
+
+* using migrations
+* using the Command line [Console Commands](../install/console-commands.md)
+
+### Creating the first Administrator during a migration
+
+This is helpful e.g. when using you Yii2 applicatio with Docker and need to start the Docker Container with basic user settings.
+
+We will create an ```admin```user with a ```adminisrator``` role. 
+
+Put this in your migration:
+
+    class m... extends Migration
+    {
+        public function safeUp()
+        {
+            $auth = Yii::$app->authManager;
+                
+            // create a role named "administrator"
+            $administratorRole = $auth->createRole('admin');
+            $administratorRole->description = 'Administrator';
+            $auth->add($administratorRole);
+
+            // create permission for certain tasks
+            $permission = $auth->createPermission('user-management');
+            $permission->description = 'User Management';
+            $auth->add($permission);
+
+            // let administrators do user management
+            $auth->addChild($administratorRole, $auth->getPermission('user-management'));
+
+            // create user "admin" with password "verysecret"
+            $user = new \Da\User\Model\User([
+                'scenario' => 'create', 
+                'email' => "email@example.com", 
+                'username' => "admin", 
+                'password' => "verysecret"  // >6 characters!
+            ]);
+            $user->confirmed_at = time();
+            $user->save();
+            
+            // assign role to our admin-user
+            $auth->assign($administratorRole, $user->id);
+        }
+
+        public function safeDown()
+        {
+            $auth = Yii::$app->authManager;
+
+            // delete permission
+            $auth->remove($auth->getPermission('user-management'));
+
+            // delete admin-user and administrator role
+            $administratorRole = $auth->getRole("administrator");
+            $user = \Da\User\Model\User::findOne(['username'=>"admin"]);
+            $auth->revoke($administratorRole, $user->id);
+            $user->delete();
+            $auth->remove($administratorRole);
+        }
+
+## User Management
+
+Having setup the ```admin``` user you can start using user management at
+
+    http://yourapp/index.php?r=user/admin
+
+You should be prompted a login screen and the enter ```admin/verysecret```.
+
+## Working with authentication
+
+Usually access restrictions to controller actions care specified in 
+[```behaviors()```](http://stuff.cebe.cc/yii2docs/guide-security-authorization.html).
+
+Additionally, in your code you can directly use permission checks. This is
+helpful e.g. in ```./views/layouts/main.php```.
+
+Examples:
+
+    // Is current user a guest (not signed in?)
+    if (Yii::$app->user->isGuest) {
+        ...
+    }
+
+    // Get roles of user
+    $roles = Yii::$app->authManager->getRolesByUser(Yii::$app->user->getId());
+
+    // Does current user have permission to do "user-management"?
+    if (Yii::$app->user->can("user-management")) {
+        ...
+    }
+
+### Recommended Reading
+
+It is helpful to basically understand how Yii2 does authantication. The you can get in Yii2-usuario more quickly.
+
+- [The Definitive Guide to Yii 2.0: Authentication](https://www.yiiframework.com/doc/guide/2.0/en/security-authentication)
+
+