Feature: Clarify that docs issues typically don't get version labels

[cmaloney]

Describe the enhancement or feature you would like

In learning how to label / triage came across a docs issue where I got the labels fairly off and I would like to add more details to the devguide to help future triagers get it right the first time. In particular:

1. docs issues don't typically get version labels (Those tend to only go with code changes)
2. If there's no code change needed then stdlib, extension-modules, etc. tend not to apply.

Describe alternatives you have considered

No response

Additional context

No response

[StanFromIreland]

See also PR #1613 which adds a section on them.