Clarify how non-Team folks can influence Chair selection

[jyasskin]

The Team appoints group chairs, and it's not obvious from either the Process or the Guide how to give input into that process or help ensure that the Team makes a good choice. I suspect that the Guide is the right place to document how to give input, probably with a link from the charter template so people can find it.

@rhiaro's https://rhiaro.co.uk/2023/09/social-web goes a little farther to suggest that a particular new WG's charter give a set of criteria for chair selection and that the "decision making process and rationale [should] be completely transparent".

[plehegar]

Related issues:

• Chair appointment community involvement, transparency, enabling objections and handling them process#281
• Self-Review Questionnaire for Chair Candidates solid/specification#568