Update documentation for v32

[DennisClark]

Review existing documentation for correctness

• installation instructions
• usage instructions
• API usage information

make sure the Changelog is complete
are there any Upgrade instructions

[TG1999]

User-

• Using the UI and API
• Explain how to use API via openAPI documentation
• A Table to show endpoint what to query it with and what you can expect from the output.
• Explain WebUI
  • Search by vulnerabilities and packages
  • PURL or fragment of PURL
  • Drill on details and all the thing shown on the package details page.

Developer -
Move importer and improver to CONTRIBUTING section

Local Instance -

• Installation
• API usage

[TG1999]

closed by #1169