Add link to Roy Fielding's paper (#1017)

* Add link to Roy Fielding's paper

The backend diagram makes reference to Roy Fielding's dissertation. I thought it would be helpful to have a direct link to his paper for convenience.

* Update 100-rest.md

Co-authored-by: Kamran Ahmed <kamranahmed.se@gmail.com>

content/roadmaps/101-backend/content/109-apis/100-rest.md

@@ -1 +1,9 @@
-# Rest
+# REST
+
+REST, or REpresentational State Transfer, is an architectural style for providing standards between computer systems on the web, making it easier for systems to communicate with each other. 
+
+<ResourceGroupTitle>Free Content</ResourceGroupTitle>
+
+<BadgeLink colorScheme='yellow' badgeText='Read' href='https://www.codecademy.com/article/what-is-rest'>What is REST?</BadgeLink>
+<BadgeLink colorScheme='yellow' badgeText='Read' href='https://www.redhat.com/en/topics/api/what-is-a-rest-api'>What is a REST API?</BadgeLink>
+<BadgeLink colorScheme='yellow' badgeText='Read' href='https://www.ics.uci.edu/~fielding/pubs/dissertation/rest_arch_style.htm'>Roy Fielding's dissertation chapter, "Representational State Transfer (REST)"</BadgeLink>