add ref

Author: gambitier

session 1/chapters/references.md

@@ -9,3 +9,5 @@
 - https://medium.com/@happymishra66/execution-context-in-javascript-319dd72e8e2c#:~:text=Execution%20context%20(EC)%20is%20defined,to%20at%20a%20particular%20time.
 
 - https://blog.bitsrc.io/javascript-internals-javascript-engine-run-time-environment-settimeout-web-api-eeed263b1617
+
+- https://hackernoon.com/understanding-js-the-event-loop-959beae3ac40