Add more CS team files to code owners (github#19954)

.github/CODEOWNERS

@@ -27,6 +27,9 @@ package.json @github/docs-engineering
 # Content strategy
 /contributing/content-markup-reference.md @github/docs-content-strategy
 /contributing/content-style-guide.md @github/docs-content-strategy
+/contributing/content-model.md @github/docs-content-strategy
+/contributing/content-style-guide.md @github/docs-content-strategy
+/contributing/content-templates.md @github/docs-content-strategy
 
 # Make sure that Octokit maintainers get notified about changes
 # relevant to the Octokit libraries (https://github.com/octokit)