01-cascade-fix: Add checkboxes to the README

Add checkboxes to the README to make the progress tracking a better experience.

Author: gs-101

foundations/cascade/01-cascade-fix/README.md

@@ -14,5 +14,5 @@ Issues with the cascade can be the bane of their existence for many when it come
 
 ### Self Check
 
-- Did you make sure to not edit the HTML file?
-- If you added selectors to the CSS, do they target a valid HTML element?
+- [ ] Did you make sure to not edit the HTML file?
+- [ ] If you added selectors to the CSS, do they target a valid HTML element?