Merge branch 'FixDocu' into 'master'

Add doxygen documentition for line source terms.

See merge request ogs/ogs!3618

Documentation/ProjectFile/prj/process_variables/process_variable/source_terms/source_term/Line/c_Line.md

+Declares a source term that is defined on a line shaped sub-domain (line mesh).
+
+The user should carefully check which physical quantity that parameter is.

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

+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

@@ -49,6 +49,9 @@ std::unique_ptr<SourceTerm> createVolumetricSourceTerm(
         volumetric_source_term_parameter_name, parameters, 1,
         &source_term_mesh);
 
+    // instruction to create documentation for the parameter
+    //! \ogs_file_param_special{prj__process_variables__process_variable__source_terms__source_term__Line__parameter}
+
     DBUG("Using '{:s}' as volumetric source term parameter.",
          volumetric_source_term.name);