Update CircleCI config to display message about using script

Author: camdecoster

.circleci/config.yml

@@ -303,6 +303,7 @@ jobs:
       - run:
           name: Compare pixels
           command: .circleci/test.sh test-image ; find build -maxdepth 1 -type f -delete
+      - image-diff-message
       - store_artifacts:
           path: build
           destination: /
@@ -317,6 +318,7 @@ jobs:
       - run:
           name: Compare pixels
           command: .circleci/test.sh test-image-virtual-webgl ; find build -maxdepth 1 -type f -delete
+      - image-diff-message
       - store_artifacts:
           path: build
           destination: /
@@ -331,6 +333,7 @@ jobs:
       - run:
           name: Compare pixels
           command: .circleci/test.sh test-image ; find build -maxdepth 1 -type f -delete
+      - image-diff-message
       - store_artifacts:
           path: build
           destination: /
@@ -345,6 +348,7 @@ jobs:
       - run:
           name: Compare pixels of mathjax v3 baselines
           command: .circleci/test.sh test-image-mathjax3
+      - image-diff-message
       - store_artifacts:
           path: build
           destination: /
@@ -515,6 +519,16 @@ jobs:
       - store_artifacts:
           path: topojson.tar
 
+commands:
+  image-diff-message:
+    steps:
+      - run:
+          name: IMAGE DIFF DETECTED - SEE NOTE BELOW
+          when: on_fail
+          command: |
+            echo "Image Diff Detected: baselines may need to be updated. Use \"circleci_image_artifact_download.sh\" to download new baselines."
+            echo "Add the new images to \"test/image/baselines\" and commit them to this pull request."
+
 workflows:
   version: 2
   build-and-test: