Update readme.md

readme.md

 ## Server-Sent Event Application with Spring Webflux
 
+learning: how server-sent event technology works.
+
+SSE provides asynchronous communication with event stream from server to the client over HTTP for web applications.
+The server can send un-directional messages/events to the client and can update the client asynchronously.
+
 ```
     curl --location --request POST 'http://localhost:8080/api/v1/live-scores' \
     --header 'Content-Type: application/json' \