[Docu] Prj. file params for volumetric source term.

Documentation/ProjectFile/prj/process_variables/process_variable/source_terms/source_term/Volumetric/c_Volumetric.md

@@ -0,0 +1,3 @@
+Declares a source term that is defined on the entire domain.
+
+The user should carefully check which physical quantity that parameter is.

Documentation/ProjectFile/prj/process_variables/process_variable/source_terms/source_term/Volumetric/t_parameter.md

@@ -0,0 +1,4 @@
+The name of the parameter that defines the value that should be used for the source
+term. Nodal parameters are not supported.
+
+The user should carefully check which physical quantity that parameter is.

ProcessLib/SourceTerms/CreateVolumetricSourceTerm.cpp

@@ -33,7 +33,7 @@ std::unique_ptr<SourceTerm> createVolumetricSourceTerm(
 
     // source term field name
     auto const& volumetric_source_term_parameter_name =
-        //! \ogs_file_param{prj__process_variables__process_variable_source_terms__volumetric_source_term__parameter}
+        //! \ogs_file_param{prj__process_variables__process_variable__source_terms__source_term__Volumetric__parameter}
         config.getConfigParameter<std::string>("parameter");
     auto& volumetric_source_term = findParameter<double>(
         volumetric_source_term_parameter_name, parameters, 1);