Merge branch 'docs-add-gpt-blog-to-ref-arch' into 'master'

Cross-link GPT blog post to Ref Architecture page

See merge request gitlab-org/gitlab!80521

doc/administration/reference_architectures/index.md

@@ -97,6 +97,7 @@ The [Quality Engineering - Enablement team](https://about.gitlab.com/handbook/en
 - Network latency on the test environments between components on all Cloud Providers were measured at <5ms. Note that this is shared as an observation and not as an implicit recommendation.
 - We aim to have a "test smart" approach where architectures tested have a good range that can also apply to others. Testing focuses on 10k Omnibus on GCP as the testing has shown this is a good bellwether for the other architectures and cloud providers as well as Cloud Native Hybrids.
 - Testing is done publicly and all results are shared.
+- For more information about performance testing at GitLab, read [how our QA team leverages GitLab’s performance testing tool (and you can too)](https://about.gitlab.com/blog/2020/02/18/how-were-building-up-performance-testing-of-gitlab/).
 
 The following table details the testing done against the reference architectures along with the frequency and results. Additional testing is continuously evaluated, and the table is updated accordingly.