Create roles for documentation

[Ira-Maier]

optional: Due to the large growth of our documentation it would be helpful to create roles to highlight which part of the documentation is helpful to whom:
roles could be:

• chemist
• contributor (to the documentation)
• developer (of docusaurus)
• system admin or creator (of docusaurus)

[JanCBrammer]

Differentiation between system-admin and instance-admin. @PiTrem, @ptrxyz, is there a distinction between those roles, and if so, what are the most fundamental differences that need to be documented? Also see #47 (comment).