Add Codex CLI connection instructions (#1171)

Added instructions for connecting with OpenAI Codex CLI.

## Overview
Added instruction for connecting MCP with Codex CLI

## Type of change

**Type:** Update existing documentation

## Related issues/PRs
 
NA

<!-- For LangChain employees, if applicable: -->
- Linear issue:
- Slack thread:

## Checklist
<!-- Put an 'x' in all boxes that apply -->
- [x] I have read the [contributing guidelines](README.md)
- [x] I have tested my changes locally using `docs dev`
- [x] All code examples have been tested and work correctly
- [x] I have used **root relative** paths for internal links
- [x] I have updated navigation in `src/docs.json` if needed
- I have gotten approval from the relevant reviewers
- (Internal team members only / optional) I have created a preview
deployment using the [Create Preview Branch
workflow](https://github.com/langchain-ai/docs/actions/workflows/create-preview-branch.yml)

## Additional notes
<!-- Any other information that would be helpful for reviewers -->

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: tom21100227

src/use-these-docs.mdx

@@ -59,6 +59,14 @@ claude mcp add --transport http docs-langchain https://docs.langchain.com/mcp
 2. Go to Settings > Connectors
 3. Add our MCP server URL: `https://docs.langchain.com/mcp`
 
+### Connect with Codex CLI
+
+If you're using OpenAI Codex CLI, run this command in your terminal to add the server globally: 
+
+```sh
+codex mcp add langchain-docs --url https://docs.langchain.com/mcp
+```
+
 ### Connect with Cursor or VS Code
 
 Add the following to your MCP settings configuration file: