Update manual testing doc with syntax highlighting check.

doc/release/manual_testing.md

@@ -29,7 +29,7 @@ Use the [support document](https://docs.google.com/document/d/1cAHvbdFE6zR5WY-zh
 ## Web editor
 - create, edit, remove file in web UI
 
-## Group 
+## Group
 - create group
 - create project in group
 - add/remove group member
@@ -38,10 +38,14 @@ Use the [support document](https://docs.google.com/document/d/1cAHvbdFE6zR5WY-zh
 ## Markdown
 - Visit / clone [relative links repository](https://dev.gitlab.org/samples/relative-links/tree/master) and see if the links are linking to the correct documents in the repository
 - Check if images are rendered in the md
-- Click on a [directory link](https://dev.gitlab.org/samples/relative-links/tree/master/documents) and see if it correctly takes to the tree view 
+- Click on a [directory link](https://dev.gitlab.org/samples/relative-links/tree/master/documents) and see if it correctly takes to the tree view
 - Click on a [file link](https://dev.gitlab.org/samples/relative-links/blob/master/documents/0.md) and see if it correctly takes to the blob view
 - Check if the links in the README when viewed as a [blob](https://dev.gitlab.org/samples/relative-links/blob/master/README.md) are correct
-- Select the "markdown" branch and check if all links point to the files within the markdown branch 
+- Select the "markdown" branch and check if all links point to the files within the markdown branch
+
+## Syntax highlighting
+- Visit/clone [language highlight repository](https://dev.gitlab.org/samples/languages-highlight)
+- Check for obvious errors in highlighting
 
 ## Upgrader
 - Upgrade from the previous release