Cross link between feature flag guidance

doc/development/documentation/styleguide.md

@@ -1055,7 +1055,7 @@ Sometimes features are shipped with feature flags, either:
 - On by default, but providing the option to turn the feature off.
 - Off by default, but providing the option to turn the feature on.
 
-When documenting feature flags for a feature, it's important that users know:
+When documenting feature flags for a feature, include:
 
 - Why a feature flag is necessary. Some of the reasons are
   [outlined in the handbook](https://about.gitlab.com/handbook/product/#alpha-beta-ga).
@@ -1080,6 +1080,9 @@ Feature.disable(:feature_flag)
 ```
 ````
 
+For guidance on developing with feature flags, see
+[Feature flags in development of GitLab](../feature_flags/index.md).
+
 ## API
 
 Here is a list of must-have items. Use them in the exact order that appears

doc/development/feature_flags/index.md

@@ -10,3 +10,6 @@ Before using feature flags for GitLab's development, read through the following:
 - [Process for using features flags](process.md).
 - [Developing with feature flags](development.md).
 - [Controlling feature flags](controls.md).
+
+When documenting feature flags, see [Feature flags](../documentation/styleguide.md#feature-flags)
+in the Documentation Style Guide.