add callout for branch protection

[s-santillan]

Thanks for improving Semgrep Docs 😀

Please ensure

• [ ] A subject matter expert (SME) reviews the content
• [ ] A technical writer reviews the content or PR
• [x] This change has no security implications or else you have pinged the security team

Here is what it looks like rendered:

[s-santillan]

Hi @r2c-david! Can you let me know if the updates work for you?