feat: Add deprecated content process documentation

documentation/README.md

@@ -18,6 +18,7 @@ If you're interested in contributing to the [NGINX documentation website](https:
 - [Managing content with Hugo](/documentation/hugo-content.md)
 - [Using include files](/documentation/include-files.md)
 - [Contributing closed content](/documentation/closed-contributions.md)
+- [Review deprecated content](/documentation/deprecated-content.md)
 
 ## Writing guidance
 

documentation/deprecated-content.md

@@ -0,0 +1,57 @@
+# Review deprecated content
+
+As part of the documentation lifecycle, the documentation team periodically removes deprecated content.
+
+Although a product may no longer be available for sale, we maintain the documentation until end of support for the benefit of its users.
+
+By removing the content, their files do not create unnecessary noise when working on documentation, nor impact the user search experience.
+
+Since we use git to track file changes, the documentation is still available by checking out an older revision of the repository.
+
+To quickly traverse git history, we have created tags corresponding to the last commit prior to the removal of the products' files.
+
+## Check out deprecated product documentation
+
+To check out deprecated product documentation, use the `git` command:
+
+```shell
+git checkout <product-tag>
+```
+
+You should replace `<product-tag>` with a tag from the following table:
+
+| Product name                           | Tag                  | Date of removal |
+| -------------------------------------- | -------------------- | --------------- |
+| NGINX App Protect WAF[^1]              | `archive-nap`        | 2025-11-05      |
+| NGINX Controller                       | `archive-controller` | 2025-10-08      |
+| NGINX Management Suite[^2]             | `archive-nms`        | 2025-10-08      |
+| NGINX Service Mesh                     | `archive-mesh`       | 2025-11-05      |
+
+## Review and add tags
+
+You can review the repository tags using the `git tag` command:
+
+```text
+➜ git tag -l
+archive-controller
+archive-mesh
+archive-nap
+archive-nms
+```
+
+To add a new tag, use the following command:
+
+```shell
+git tag -a <tag-name> <commit-sha>
+```
+
+The tag name should follow the format of _archive-\<product-name\>_, and the commit sha should be the last commit **before** the content was removed.
+
+To add the new tag to the remote repository, you must add it as an explicit argument to `git push`:
+
+```shell
+git push origin <tag-name>
+```
+
+[^1]: NGINX App Protect WAF is now known as F5 WAF for NGINX  
+[^2]: NGINX Management Suite was refactored into NGINX Instance Manager