Added Flexbox Froggy - CSS Game (#9894)

* Adding Flexbox Froggy

* Removed trailing slash

* Credits

Co-authored-by: Leithen <lcrider@cvent.com>

---------

Co-authored-by: Leithen <lcrider@cvent.com>

more/free-programming-playgrounds.md

@@ -157,6 +157,7 @@
 * [CodePen](https://codepen.io)
 * [CSSdeck](https://cssdeck.com)
 * [Dabblet](https://dabblet.com)
+* [Flexbox Froggy](https://flexboxfroggy.com) - Codepip
 * [Flexy Boxes](https://the-echoplex.net/flexyboxes/)
 * [SoloLearn](https://code.sololearn.com/web#css)
 * [Tailwind Play](https://play.tailwindcss.com)