Merge branch 'docs-nfriend-add-deprecation-guideline' into 'master'

Add deprecation guideline to development documentation

See merge request gitlab-org/gitlab!30746

doc/development/README.md

@@ -145,6 +145,10 @@ See [database guidelines](database/index.md).
 
 - [Refactoring guidelines](refactoring_guide/index.md)
 
+## Deprecation guides
+
+- [Deprecation guidelines](deprecation_guidelines/index.md)
+
 ## Documentation guides
 
 - [Writing documentation](documentation/index.md)

doc/development/deprecation_guidelines/index.md

+# Deprecation guidelines
+
+This page includes information about how and when to remove or make breaking
+changes to GitLab features.
+
+## Terminology
+
+It's important to understand the difference between **deprecation** and
+**removal**:
+
+**Deprecation** is the process of flagging/marking/announcing that a feature
+will be removed in a future version of GitLab.
+
+**Removal** is the process of actually removing a feature that was previously
+deprecated.
+
+## When can a feature be deprecated?
+
+A feature can be deprecated at any time, provided there is a viable alternative.
+
+## When can a feature be removed/changed?
+
+See our [Release and Maintenance policy](../../policy/maintenance.md).