document interaction of changelog tags with orderly_config.yml

[jeffeaton]

The changelog vignette does not describe how the changelog should be configured in orderly_config.yml and how the tags interact with the config.

It would be helpful for this to be documented.

Here's what Rich told me about them:

they should be defined in the orderly_config.yml

so for VIMC we have:

changelog:
 internal:
   public: false
 external:
   public: true

The public or not affects you only if you set up orderly web with external users