Because used in caps, these words have special meaning which I think is useful to understand. Certainly I went for a while wondering why people were randomly capitalising words in repos until I found one repo that linked to the RFC.

Similar to what's [here](https://github.com/gds-operations/open-source-guidelines/blob/master/README.md).

If they weren't capitalised, they wouldn't carry the special meaning. But if we do intend a special meaning, it's good to clarify what that is.