Add update FMI Project rules after Confirmation by MA Assembly

[chrbertsch]

Changed FMI Project Rules (approved by the MA, to be confirmed by MA Assembly):

Summary: Project members are divided into three groups with a hierarchy of duties and rights: "Steering Committee Members" are a subset of "Contributing Members" which are a subset of "Advisory Commitee Members".

New Project Rules: https://github.com/chrbertsch/fmi-standard.org/blob/add-project-rules/content/project-rules.md

Changes:

[chrbertsch]

Done with #588