Write a CNAME file on every docs deploy (#293)

Author: milancurcic

.github/workflows/docs.yml

@@ -39,6 +39,7 @@ jobs:
         cp -r docs/_build/html/* gh-pages/
         cd gh-pages
         touch .nojekyll
+        echo clouddrift.org > CNAME
         git config --local user.email "[email protected]"
         git config --local user.name "GitHub Action"
         git add .