Clarify optional parameters for two more files

Author: tsmbland

docs/inputs/commodities.rst

@@ -16,7 +16,11 @@ a whole are defined in a csv file with the following structure.
    Agricultural-residues, Energy, agrires, 112, 15.4, PJ
 
 Commodity
-   represents the extended name of a commodity
+   represents the extended name of a commodity (e.g. "Heating" or "Electricity").
+
+CommodityName
+   the internal name used for a commodity inside the model (e.g. "heat" or "elec").
+   Any references to commodities in other files must use these names.
 
 CommodityType
    defines the type of a commodity (i.e. Energy, Service, Material, or Environmental).
@@ -32,23 +36,16 @@ CommodityType
    The "environmental" type refers to non-energy commodities whichare used to quantify an impact on the environment,
    such as greenhouse gases or CO2. They can be subjected to different types of environmental fees or taxes.
 
-CommodityName
-   is the internal name used for a commodity inside the model.
-
-CommodityEmissionFactor_CO2
+CommodityEmissionFactor_CO2 (optional)
    is CO2 emission per unit of commodity flow.
    This commodity property is not directly used in the MUSE core set of equations, but can be further referred to
    for any subsequent development of the code.
 
-HeatRate
+HeatRate (optional)
    represents the lower heating value of an energy commodity
    This commodity property is not directly used in the MUSE core set of equations, but can be further referred to
    for any subsequent development of the code.
 
-Unit
+Unit (optional)
    is the unit used as a basis for all the input data. More specifically the model allows
-   a totally flexible way of defining the commodities. CommodityName is currently the
-   only column used internally as it defines the names of commodities and needs to be
-   used consistently across all the input data files. The remaining columns of the file
-   are only relevant for the user internal reference for the original sets of
-   assumptions used.
+   a totally flexible way of defining the commodities.

docs/inputs/existing_capacity.rst

@@ -24,7 +24,7 @@ ProcessName
 RegionName
    represents the region ID and needs to be consistent across all the data inputs.
 
-Unit
+Unit (optional)
    reports the unit of the technology capacity; it is for the user internal reference only.
 
 2010,..., 2050