fix/readme with detailed info

Author: alejandroereyesb

README.md

@@ -2,9 +2,9 @@
 
 In this repository you will find a selection of challenges to do with HTML & CSS.
 
-## [Zoo CSS challenge](./zoo-css-challenge/README.md)
+## [Zoo CSS challenge](./zoo-css-challenge/)
 Exercise about CSS selectors and basic CSS properties.
-## [Two truths one lie](./Two-Truths-One-Lie/README.md)
+## [Two truths one lie](./Two-Truths-One-Lie)
 Exercise about Mobile first design with Flexbox and Media Queries.
-## [Form controls](./Form-Controls/README.md)
+## [Form controls](./Form-Controls)
 Exercise about styling forms with CSS.