docs: add gateways and proxies section to README

[nickytonline]

Proposed changes

As per you comment in #416 @kmruiz, I've submitted a PR to get the ball rolling. This PR adds a gateways and proxies section to the README docs.

Closes #416

Checklist

• I have signed the MongoDB CLA

[nickytonline]

Also, just an FYI, I'm n on PTO this coming week so won't be able to address any feedback until the end of next week.

[kmruiz]

Hi @nickytonline !

Thanks for opening the PR. I've been reviewing it and so far it looks good. I've added a few changes to clarify that having these examples in the README.md do not:

• Endorse any third party.
• They are not enough in terms of security best practices and should be reviewed.
• We provide them in a best-effort basis and we don't do technical support on them (delegated to the actual third-party).

I'll ask other teammates to review this and if everything looks fine for them too, we'll merge it and close the underlying issue.

Thanks a lot for your contribution and enjoy your PTO!

[Copilot]

Pull Request Overview

This PR enhances the README documentation by replacing a basic proxy support section with a comprehensive "Gateways and Proxies" section that covers both inbound authentication security and outbound proxy configuration.

• Reorganizes proxy documentation with better structure and security guidance
• Adds detailed information about authentication gateways like Pomerium for securing remote MCP deployments
• Expands proxy configuration examples with environment variables and usage instructions

Comments suppressed due to low confidence (1)