Add unit of outputs in runorder.md

[epingchris]

It would be perhaps useful to state explicitly on the runorder.md doc file what the units of important output variables are.

In particular, the output of this step, carbon density, is in Mg C/ha if I'm not mistaken:

python3 -m methods.inputs.generate_carbon_density --buffer /data/tmf/123/buffer.geojson \
                                                --luc /data/tmf/123/luc.tif \
                                                --output /data/tmf/123/carbon-density.csv

(And perhaps it'd be more precise to call it 'ACD' instead of 'AGB' data layers)

And the output of this step, additionality, is in Mg CO2e if I'm not mistaken:

python3 -m methods.outputs.calculate_additionality --project /data/tmf/project_boundaries/123.geojson \
                                                    --project_start 2012
                                                    --evaluation_year 2021 \
                                                    --density /data/tmf/123/carbon-density.csv \
                                                    --matches /data/tmf/123/pairs \
                                                    --output /data/tmf/123/additionality.csv

[mdales]

I suspect these are currently done to match the methodology document?