Update 120-real-time-data.md (#5782)

Added links to pages containing brief explanations on the topics listed here.

src/data/roadmaps/backend/content/120-real-time-data.md

@@ -5,4 +5,7 @@ There are many ways to get real time data from the backend. Some of them are:
 - Websockets
 - Server Sent Events
 - Long Polling
-- Short Polling
+- Short Polling
+
+- [Introduction to HTTP Polling and Web Sockets](https://www.youtube.com/watch?v=OsgrJDMPl58)
+- [Introduction to Long Polling](https://www.pubnub.com/guides/long-polling/)