add contents to documentation repository

Please add the remaining documentation here: https://codebase.helmholtz.cloud/hmc/hmc-public/FAIR-dashboard/documentation/-/tree/development/pages?ref_type=heads

• Tab: "Dashboard"
  • Section: "Overview" (done)
  • Section: "How to" (to do)
    • Installation and startup (copy from dashboard-readme, to do)
    • Modify and add contents (text, figures, hyperlinks, in particular what HMC-specific parts need to be exchanged, to do)
    • Modify and add pages (to do)
    • Modify and add new plots (to do)
  • Section: "Design decisions" (Technical explanations and challenges faced, to do)
    • including "Data model" (describing database structure, to do)
  • Section: "Technical documentation" (to do)
    • link to reference documentation - for now use manually created documentation of classes, functions and methods, to do)