Document labels for issues and PRs

[magnusbaeck]

Description

We've recently started to use a couple of issue/PR labels (protocol and protocol-incompat), partly for general filtering but also to be able to generate release notes automatically. However, labeling issues and PRs correctly requires that we have a common understanding of what they actually mean. Let's document what the labels mean. Perhaps we can get away with simply good label descriptions at https://github.com/eiffel-community/eiffel/labels, otherwise we'll have to create or amend a Markdown document.

Motivation

If we ask people to categorize issues and PRs there should be guidance so that labels are applied consistently.

Exemplification

N/A

Benefits

More accurate labels

Possible Drawbacks

There's no immediately obvious documentation location besides the description of the label itself, but if that's deemed insufficient we might end up with documentation that's hard to find and mostly piles onto the maintenance burden.

[magnusbaeck]

Questions that have come up:

• Should we create a documentation label? Example Move usage-examples into examples #226
• When should we use the protocol label? What about
  • JSON schema doesn't have link objects validations for Eiffel events  #148
  • Ambiguous description of SCS's data.change.id field #223