rg: Only list matched files (#2302)

pages/common/rg.md

@@ -21,3 +21,7 @@
 - Search for a pattern in files matching a glob (e.g., `README.*`):
 
 `rg {{pattern}} -g {{glob}}`
+
+- Only list matched files -- useful when piping to other commands:
+
+`rg --files-with-matches {{pattern}}`