docs(gitlab): add official doc link.

Author: appleboy

installation/install-with-gitlab.md

@@ -1,19 +1,21 @@
 # Install Drone with GitLab
 
+See the online documentaion: [Single Machine](https://docs.drone.io/installation/gitlab/single-machine/) | [Multi-Machine](https://docs.drone.io/installation/gitlab/multi-machine/)
+
 ## How to register OAuth application
 
 Go to your GitLab [profile setting](https://gitlab.com/profile) and navigate to your account settings and choose `Applications` from the menu.
 
-<img src="images/gitlab-setup-01.png" />
+![gitlab-setup-01](images/gitlab-setup-01.png)
 
 Please make sure that your drone `Redirect URI` setting. It is very import the authorization callback URL matches your http(s) scheme and hostname exactly with **/authorize** (0.8) **/login** (1.0) as the path.
 
-<img src="images/gitlab-setup-02.png" />
+![gitlab-setup-02](images/gitlab-setup-02.png)
 
 Copy `Application ID` and `Secret`
 
-<img src="images/gitlab-setup-03.png" />
+![gitlab-setup-03](images/gitlab-setup-03.png)
 
 Open your drone home page in your browser and login as gitlab account.
 
-<img src="images/gitlab-setup-04.png" />
+![gitlab-setup-04](images/gitlab-setup-04.png)