go: document adding C function calls to CPU profiles

[nsrip-dd]

What does this PR do?

Documents how to add C function call information to Go's CPU profiles.

Motivation

Go's CPU profiles lack detailed information on time spent running C code. There is an optional extension interface to add more detail, and one of the Go maintainers has released a library which implements some of this interface. It is experimental and has some known issues, but it's still mostly usable. We should let our users know it exists, since they might wonder why they don't see C code in their profiles if they expect to.

Additional Notes

---

Reviewer checklist

• [ ] Review the changed files.
• [ ] Review the URLs listed in the Preview section.
• [ ] Check images for PII
• [ ] Review any mentions of "Contact Datadog support" for internal support documentation.

[github-actions[bot]]

Preview links (active after the build_preview check completes)

Modified Files

• https://docs-staging.datadoghq.com/nick.ripley/cgo-profile-frames/profiler/enabling/go