[docs] Refactor QualGroup.rst: add membership rules, restructure sections (#157804)
This patch updates the LLVM Qualification Group documentation to reflect
current group structure and practices:
- Restructures the **Group Composition** section (previously
"Participation" + "Contributors")
- Adds a formal **member table** with affiliations and community handles
- Introduces **participation principles**
- Documents **membership criteria**, **nomination process**, and
**review cycle**
- Corrects references to **meeting materials** (wrong path)
These changes aim to improve clarity, inclusiveness, and alignment with
similar working groups (e.g., LLVM Security Response Team).
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Co-authored-by: Wendi Urribarri (Woven by Toyota <wendi.urribarri@woven-planet.global>