Add alternative steps extension to documentation (#1074)

docs/extensions.html

@@ -33,6 +33,11 @@ extensions:
   slug: bulma-steps
   width: 989
   height: 89
+- name: bulma-steps (alternative)
+  url: https://aramvisser.github.io/bulma-steps/
+  slug: bulma-steps-alternative
+  width: 752
+  height: 101
 - name: bulma-tooltip
   url: https://github.com/Wikiki/bulma-tooltip
   slug: bulma-tooltip