Add generated reference guidance to the README #98

Context and request

NerdFonts users need a clear path from the module landing page to the complete generated command reference and to in-shell help examples.

Acceptance criteria

• README.md links to the published NerdFonts reference documentation.
• README.md shows commands that list the module's commands and open example help for a real command.
• Existing installation, usage, cache, update, and uninstall guidance remains unchanged.

Constraints and non-goals

• Keep the change limited to the README landing page; do not alter module behavior or generated command help.
• Retain the existing user-task guidance rather than replacing it with a minimal landing page.

Technical decisions

The README.md landing page retains its task-oriented guidance. Generated comment-based help remains the canonical per-command reference at psmodule.io/NerdFonts.

Implementation plan

• Validate the existing README narrative against the current main branch and the module documentation model.
• Add a concise Documentation section in README.md with the published reference link and PowerShell discovery commands.
• Integrate current main non-destructively and verify the branch diff contains only the intended README addition.
• Run repository documentation checks and request an automated review round.