cheat.sh added in All-in-one Cheat sheet section

I have added cheat.sh in All-in-one section. 
This link is very useful to get all-cheats in one place.

README.md

@@ -943,6 +943,8 @@ performance of any of your sites from across the globe.<br>
 &nbsp;&nbsp;:small_orange_diamond: <a href="https://devhints.io/"><b>Rico's cheatsheets</b></a> - this is a modest collection of cheatsheets.<br>
 &nbsp;&nbsp;:small_orange_diamond: <a href="https://devdocs.io/"><b>DevDocs API</b></a> - combines multiple API documentations in a fast, organized, and searchable interface.<br>
 </p>
+&nbsp;&nbsp;:small_orange_diamond: <a href="https://cheat.sh/"><b>cheat.sh</b></a> - The only cheat sheet you need.<br>
+</p>
 
 ##### :black_small_square: Other