[Doc] added docu file stubs

...ation/ProjectFile/process/convergence_criterion/t_type.md

...File/process/secondary_variables/i_secondary_variables.md

...secondary_variables/secondary_variable/a_internal_name.md

...s/secondary_variables/secondary_variable/a_output_name.md

...cess/secondary_variables/secondary_variable/a_sink_arg.md

...ss/secondary_variables/secondary_variable/a_source_fct.md

.../process/secondary_variables/secondary_variable/a_type.md

...dary_variables/secondary_variable/i_secondary_variable.md

.../process/secondary_variables/secondary_variable/t_plug.md