STASH code to CF name translations: photolysis and nmvoc additions

[jhemmings]

I propose these changes to Metarelate's metOcean knowledge base.
The changes are correct, to the best of my knowledge.
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Copy of text in the uploaded file:

|STASH(msi)|CFName|units|force_update(y/n)|
|m01s50i228|photolysis_rate_of_ozone_to_1D_oxygen_atom|s-1|n|
|m01s50i229|photolysis_rate_of_nitrogen_dioxide|s-1|n|
|m01s50i230|mass_concentration_of_nmvoc_expressed_as_carbon_in_air|ug m-3|n|

[marqh]

merged and adopted with thanks

pushed to Iris in
SciTools/iris#3011