docs: another injection query example (#13312)

Author: gruhn

book/src/guides/injection.md

@@ -4,11 +4,16 @@ Writing language injection queries allows one to highlight a specific node as a
 In addition to the [standard][upstream-docs] language injection options used by tree-sitter, there
 are a few Helix specific extensions that allow for more control.
 
-And example of a simple query that would highlight all strings as bash in Nix:
+An example of a simple query that would highlight all strings as bash in Nix:
 ```scm
 ((string_expression (string_fragment) @injection.content)
   (#set! injection.language "bash"))
 ```
+Another example is this query, which highlights links in comments and keywords like "TODO", by reusing the dedicated "comment" language:
+```
+((comment) @injection.content
+  (#set! injection.language "comment"))
+```
 
 ## Capture Types