Report sha256sum information

Co-authored-by: Meghan Jones <meghanj@alum.mit.edu>

Author: seisman

.github/workflows/release-baseline-images.yml

@@ -31,6 +31,7 @@ jobs:
         mkdir baseline-images
         mv pygmt/tests/baseline/*.png baseline-images/
         zip -r baseline-images.zip baseline-images
+        shasum -a 256 baseline-images.zip
 
     - name: Upload baseline image as a release asset
       uses: shogo82148/actions-upload-release-asset@v1.3.0