Add Gremlin cheatsheet and Graphs group (#10824)

* Update free-programming-books-langs.md

* Update free-programming-books-langs.md

Adjust Spacing between headers and sections

* Update free-programming-playgrounds.md with Gremlin

Add Gremlin Playground reference

* Update free-programming-playgrounds.md

* Add Gramlin Cheatsheets and Samples

* Add gremlin cheatsheets and samples

more/free-programming-cheatsheets.md

@@ -13,7 +13,9 @@
 * [Docker](#docker)
 * [Git](#git)
 * [Go](#go)
-* [GraphQL](#graphql)
+* [Graphs](#graphs)
+    * [GraphQL](#graphql)
+    * [Gremlin](#gremlin)
 * [HTML and CSS](#html-and-css)
 * [IDE and editors](#ide-and-editors)
 * [Java](#java)
@@ -177,7 +179,9 @@
 * [গো \| ডেভ সংকেত<](https://devsonket.com/go) - devsonket (HTML)
 
 
-### GraphQL
+### Graphs
+
+#### GraphQL
 
 * [GraphQL Cheat Sheet](https://licor.me/post/graphql) - Chuanrong Li (HTML)
 * [GraphQL Cheat Sheet](https://cheatsheetseries.owasp.org/cheatsheets/GraphQL_Cheat_Sheet.html) - Jim Manico, Jakub Maćkowski (HTML)
@@ -185,6 +189,13 @@
 * [GraphQL Cheatsheet](https://devhints.io/graphql) - devhints, Rico Santa Cruz (HTML)
 
 
+#### Gremlin
+
+* [Gremlin 101 Cheatsheet](https://dkuppitz.github.io/gremlin-cheat-sheet/101.html) - Daniel Kuppitz (HTML)
+* [Gremlin 102 Cheatsheet](https://dkuppitz.github.io/gremlin-cheat-sheet/102.html) - Daniel Kuppitz (HTML)
+* [Gremlin Recipes](https://tinkerpop.apache.org/docs/3.3.2/recipes/) - Apache Tinkerpop (HTML)
+
+
 ### HTML and CSS
 
 * [Accessibility CheatSheet](https://learn-the-web.algonquindesign.ca/topics/accessibility-cheat-sheet/) - Algonquin Design (HTML)