DOC: updated the heading levels accordingly

src/doc/high_level_api.rst

@@ -25,7 +25,7 @@ Or to speak it out directly in Python:
    print(obj.r + 25) # getting properties (new api)
 
 Quickstart
-==========
+----------
 
 The module, needed for the high level API is called:
 caosdb.high\ :sub:`levelapi`
@@ -115,7 +115,7 @@ statement:
    print(str(obj))
 
 Concepts
-========
+--------
 
 As described in the section Quickstart the two functions
 "convert\ :sub:`topythonobject`" and "convert\ :sub:`toentity`" convert