04-flex-information: Add checkboxes to the README

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

Author: gs-101

foundations/flex/04-flex-information/README.md

@@ -10,10 +10,10 @@ For this one you will need to edit the HTML a little bit too. We can't be making
 
 ### Self Check
 
-- All items are centered on the page (horizontally, not vertically).
-- The title is centered on the page.
-- There is 32px between the title and the 'items.'
-- There is 52px between each item.
-- The items are arranged horizontally on the page.
-- The items are only 200px wide and the text wraps.
-- The item text is centered.
+- [ ] All items are centered on the page (horizontally, not vertically).
+- [ ] The title is centered on the page.
+- [ ] There is 32px between the title and the 'items.'
+- [ ] There is 52px between each item.
+- [ ] The items are arranged horizontally on the page.
+- [ ] The items are only 200px wide and the text wraps.
+- [ ] The item text is centered.