Use plain markdown for app store images

appinfo/info.xml

@@ -21,15 +21,15 @@
 
 This app is based on the G DATA Verdict as a Service (VaaS) API. To get started with the app, you have to register via our [registration page](https://account-staging.gdata.de/realms/vaas-staging/login-actions/registration?client_id=landing-page&tab_id=VDSGSP4oQL0).
 
-<img style="display: block; margin: auto; height: 500px;" src="https://raw.githubusercontent.com/GDATASoftwareAG/nextcloud-gdata-antivirus/main/img/vaas-registration.png" />
+![Image](https://raw.githubusercontent.com/GDATASoftwareAG/nextcloud-gdata-antivirus/main/img/vaas-registration.png)
 
 After the registration you can use these credentials within your nextcloud installation. To do this go to your Administration Settings.
 
-<img style="display: block; margin: auto; height: 500px;" src="https://raw.githubusercontent.com/GDATASoftwareAG/nextcloud-gdata-antivirus/main/img/administration-settings.png" />
+![Image](https://raw.githubusercontent.com/GDATASoftwareAG/nextcloud-gdata-antivirus/main/img/administration-settings.png)
 
 There you will find the "Verdict-as-a-Service" section under the "Administration" section.
 
-<img style="display: block; margin: auto; height: 500px;" src="https://raw.githubusercontent.com/GDATASoftwareAG/nextcloud-gdata-antivirus/main/img/verdict-as-a-service-section.png" />
+![Image](https://raw.githubusercontent.com/GDATASoftwareAG/nextcloud-gdata-antivirus/main/img/verdict-as-a-service-section.png)
 
 Please make sure the "Authentication Method" "Resource Owner Password Flow" is selected. Now you can put your credentials into the 'username' and 'password' field and click save afterwards.
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