Clarify some documentation

Author: NlightNFotis

src/goto-harness/goto_harness_parse_options.cpp

@@ -30,7 +30,10 @@ Author: Diffblue Ltd.
 // sequence of events:
 // 1. Initialise a goto-model by parsing an input (goto) binary
 // 2. Initialise the harness generator (with some config) that will handle
-//    the mutation of the goto-model.
+//    the mutation of the goto-model. The generator should create a new
+//    function that can be called by `cbmc --function`. The generated function
+//    should implement the behaviour of the harness (What exactly this means
+//    depends on the configuration)
 // 3. Write the end result of that process to the output binary
 
 int goto_harness_parse_optionst::doit()