Update howto_contribute.md

doc.zih.tu-dresden.de/docs/contrib/howto_contribute.md

@@ -14,9 +14,9 @@ For that, open an issue to report typos and missing documentation or request for
 wording etc. ZIH staff will get in touch with you to resolve the issue and improve the
 documentation.
 
-??? tip "Create a GitLab issue"
+??? tip "Create an issue in GitLab"
 
-    ![Something](misc/create_gitlab_issue.gif)
+    ![GIF showing how to create an issue in GitLab](misc/create_gitlab_issue.gif)
     {: align=center}
 
 !!! warning "HPC support"
@@ -48,4 +48,4 @@ refer to the corresponding documentation for further information.
 For experienced Git users, we provide a Docker container that includes all checks of the CI engine
 used in the back-end. Using them should ensure that merge requests will not be blocked
 due to automatic checking.
-For details, refer to the page [Work Locally Using Containers](contribute_container.md).
\ No newline at end of file
+For details, refer to the page [Work Locally Using Containers](contribute_container.md).