Merge branch 'caching-guide' into 'master'

Add caching guidelines

See merge request gitlab-org/gitlab!63971

doc/development/index.md

@@ -257,6 +257,7 @@ the [reviewer values](https://about.gitlab.com/handbook/engineering/workflow/rev
   environments.
 - [Performance guidelines](performance.md) for writing code, benchmarks, and
   certain patterns to avoid.
+- [Caching guidelines](caching.md) for using caching in Rails under a GitLab environment.
 - [Merge request performance guidelines](merge_request_performance_guidelines.md)
   for ensuring merge requests do not negatively impact GitLab performance
 - [Profiling](profiling.md) a URL, measuring performance using Sherlock, or