adds text before schema

docs/schema.rst

 Schema
 ===============
-Hier ist ein tolles Schema ...
+
+In the following code block, you can see an exemplary JSON schema of a QCF file, which can be used for the quality control of an 
+additively manufactured object. It defines customizations and requirements. The schema may look different for other 
+processes and application areas.
+
 
 .. code-block:: JSON