Update README.md to hyperlink Open AI Codex installation guide

[s-sanjay]

Update README.md for installation guide

Summary

This guide was already added as part of #1340. Update README.md to point to this

Why

There is no direct link to installation from README.md, this can lead to confusion.
Fixes # N/A

What changed

• N/A

MCP impact

• No tool or API changes

Prompts tested (tool changes only)

• No need to test

Security / limits

• No security or limits impact
• Auth / permissions considered
• Data exposure, filtering, or token/size limits considered

Tool renaming

• I am renaming tools as part of this PR (e.g. a part of a consolidation effort)
• I have added the new tool aliases in deprecated_tool_aliases.go
• I am not renaming tools as part of this PR

Note: if you're renaming tools, you must add the tool aliases. For more information on how to do so, please refer to the official docs.

Lint & tests

Just README.md update

Docs

• Not needed
• Updated (README / docs / examples)