Include the "Manage test reporting" article in the Reporters block. (#1735)

Evidently "Reporter" doesn't qualify as `ends_with("Reporter")` when pkgdown builds the site. This leads to confusing documentation that doesn't describe what a Reporter is in general.

Author: jonthegeek

_pkgdown.yml

@@ -62,6 +62,7 @@ reference:
 
 - title: Reporters
   contents:
+  - Reporter
   - ends_with("Reporter")
 
 - title: Mocking