Docs/headers and readme

[kmilodenisglez]

This pull request introduces several important project documentation files and adds SPDX license identifiers to all Python source files in the src/fabric_shim package. These changes improve the project's clarity, compliance, and transparency for contributors and users.

Documentation and Policy Additions:

• Added a new README.md with improved project description, documentation links, build instructions, and community resources.
• Added CODE_OF_CONDUCT.md outlining expected behavior and licensing for contributions.
• Added SECURITY.md to describe the security vulnerability reporting process and responsible disclosure policy.
• Added CHANGELOG.md to document release notes and changes.
• Added ADOPTERS.md to allow organizations using the project to list themselves publicly.
• Added NOTICE file with copyright, license, and attribution information.

License Compliance:

• Added SPDX license identifiers to all Python files in the src/fabric_shim package to clarify licensing and improve compliance. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]