Fix headers in workflow.rst

Author: franzpoeschel

docs/source/usage/workflow.rst

@@ -1,7 +1,10 @@
 .. _workflow:
 
+Workflow
+========
+
 Access modes
-============
+------------
 
 The openPMD-api distinguishes between a number of different access modes:
 
@@ -60,8 +63,6 @@ The openPMD-api distinguishes between a number of different access modes:
   It is a user's responsibility to ensure that the appended dataset and the appended-to dataset are compatible with each other.
   The results of using incompatible backend configurations are undefined.
 
-Workflow
-========
 
 Deferred Data API Contract
 --------------------------