Update Programming Playground with Gremlin section and reference (#10708)

* Update Programming Playground with Gremlin

* Revert Asterisk from dash

* Revert Changes and keep only required change.

* Revert Changes

more/free-programming-playgrounds.md

@@ -17,6 +17,7 @@
 * [GDScript](#gdscript)
 * [Git](#git)
 * [Go](#go)
+* [Gremlin](#gremlin)
 * [Haskell](#haskell)
 * [HTML and CSS](#html-and-css)
 * [Ionic](#ionic)
@@ -158,6 +159,11 @@
 * [SoloLearn](https://code.sololearn.com/go)
 
 
+### Gremlin
+
+* [Gremlify](https://gremlify.com)
+
+
 ### Haskell
 
 * [Try Haskell](https://www.tryhaskell.org)