Update README.md

[teamtrytenet]

Add Tenet to Agent Firewalls & Gateways (Runtime Protection).

[secxena]

Thanks for the submission. This list focuses on open-source tools, and Tenet appears to be a commercial hosted product without a public source repository. If there is an open-source component (SDK, proxy, policy engine), please link that instead and we will take another look. The diff also introduces stray blank lines that would need cleaning up.

[teamtrytenet]

Hey really appreciate your time. Our SDK is public under MIT, but it's primarily a client for our hosted service, so a decline now makes sense if it doesn't match the purpose of the list. If you ever add a hosted/commercial section, or if we open-source more of the stack down the road, we'll resubmit. Out of curiosity, since you see so much of space, do you get the sense teams are really wanting a self-hostable open-source enforcement layer? Would help us understand the need. Thanks for maintaining the list!