Fix broken links in README.md

Author: buehlefs

README.md

@@ -6,8 +6,8 @@ The QHAna Backend API is implemented in [Ballerina](https://ballerina.io) (Swan
 
 Please use the following resources to make yourself familiar with Ballerina:
 
-  * [Installation instructions](https://ballerina.io/learn/user-guide/getting-started/setting-up-ballerina/)
-  * [Hello world](https://ballerina.io/learn/user-guide/getting-started/writing-your-first-ballerina-program/)
+  * [Installation instructions](https://ballerina.io/downloads/installation-options/)
+  * [Hello world](https://ballerina.io/learn/get-started/)
   * [General documentation](https://ballerina.io/learn/)
   * [Video introduction fo language features](https://www.youtube.com/watch?v=My_uqtHvXV8&list=PL7JOecNWBb0KX8RGAjF-oRknb_YIYN-dR)