diff --git a/src/testdir/README.txt b/src/testdir/README.txt
index 203c324..c7067ac 100644
--- a/src/testdir/README.txt
+++ b/src/testdir/README.txt
@@ -162,6 +162,8 @@
 
 VIEWING GENERATED SCREENDUMPS (submitted for a pull request):
 
+Note: There is also a "git difftool" extension described in ./commondumps.vim.
+
 First, you need to check out the topic branch with the proposed changes and
 write down a difference list between the HEAD commit (index) and its parent
 commit with respect to the changed "dumps" filenames: