Draft defintion of steering committee

[tychonievich]

Resolve #572 by defining what the steering committee is, how it operates, and how people join it.

[tychonievich]

A few considerations/questions:

• I open with "The GEDCOM Standard" but debated "The FamilySearch GEDCOM standard" (which would limit our scope to 7.0 and later) or "The GEDCOM Standards" (if we want to think of the various versions as being separate standards).
• I considered adding something like "The GEDCOM Steering Committee was initially formed by FamilySearch from volunteers representing several companies and groups."
• I considered adding something about the relationship between FamilySearch and the steering committee, but didn't know what to say.