add a little

doc/source/users_guide/adding-components.rst

@@ -6,6 +6,12 @@ Adding components
 
 Here are the steps to add prognostic components to CIME models.  
 
+There are a couple of aspects of a component interface to CIME, the
+scripts interface which controls setting up component inputs and
+building the component and the run interface which controls connecting
+the component to the coupler and through the coupler, the other
+components of the CIME based model.
+
 The component should have a subdirectory **cime_config** and this
 subdirectory should have two files **buildnml** and **buildlib** The
 **buildnml** script is used to build the components instructional,
@@ -21,4 +27,10 @@ line, it is called in the case.build step and is expected to build the
 the buildlib script will be called with three arguments in order they
 are caseroot, libroot (the location of the installed library,
 typically EXEROOT/lib) and bldroot, the location of the component
-build directory.
+build directory.  Look at the cime internal components such as datm
+for an example.
+
+The coupler interface is dependent on which coupler is used, for the mct coupler in cime
+the component model must provide NNN_INIT_MCT, NNN_RUN_MCT, NNN_FINAL_MCT where NNN is the
+component type of the particular component (eg ATM for an atmosphere, LND for a land model)
+these subroutines are expected to be in the component library.