Updating the README re pdifftests

hammerlab · Nov 13, 2014 · d645307 · d645307
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commit d645307
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diff --git a/README.md b/README.md
@@ -141,4 +141,15 @@ CycleDash uses dpxdt for perceptual diff testing. To update the reference screen
 dpxdt update __tests__/pdifftests
 ```
 
+To determine whether there are any pixels that have changed before/after, and to
+generate a perceptual diff that will make it clear where the changes are, use
+the following command:
+
+*Note*: you will need to have imagemagick installed for the following command to
+succeed.
+
+```
+dpxdt test __tests__/pdifftests
+```
+
 Running `git status` after this should indicate whether the screenshots have changed.