Refactor license doc

- Add section on missing license
- Move images in a separate directory

[ci skip]

doc/license/README.md

 # Installing your license
 
-To activate all GitLab Enterprise Edition functionality, you need to upload a license.
-Once you've received your license from GitLab Inc., you can upload it by signing into your GitLab instance as an admin, and navigating to **Admin Area > License**.
+To activate all GitLab Enterprise Edition functionality, you need to upload a
+license. Once you've received your license from GitLab Inc., you can upload it
+by signing into your GitLab instance as an admin, and navigating to
+**Admin Area > License**.
 
 If you've received a `.gitlab-license` file, you can upload it directly.
 
-![upload.png](upload.png)
+![upload.png](img/upload.png)
 
-If you've received your license as plain text, you need to select the "Enter license key" option, copy the license and paste it into the "License key" field.
+If you've received your license as plain text, you need to select the
+"Enter license key" option, copy the license and paste it into the "License key"
+field.
 
-![enter.png](enter.png)
+![enter.png](img/enter.png)
 
-Once you've uploaded your license, all GitLab Enterprise Edition functionality will be active until the end of the license period.
+Once you've uploaded your license, all GitLab Enterprise Edition functionality
+will be active until the end of the license period.
 
-You can review the license details at any time in the License section of the Admin Area.
+You can review the license details at any time in the License section of the
+Admin Area.
 
-![details.png](details.png)
+![details.png](img/details.png)
+
+## What happens when my license expires?
+
+In case your license expires, you will not be able to push any commits to
+GitLab and creation of new issues and merge requests will be disabled.
+
+A message to inform of the locked state of GitLab will be presented to
+admins only.
+
+![No license message](img/no_license_message.png)