update readme

CSV/README.txt

+Chih-Yuan Lin
+2021-09-23
+-----------------------------------------------------------------------------------------
+These files contain extracted timestamps of certain types of traffic for certain scenarios.
+They are for our own (spare) research-use purpose, so those numbers may not be meaningful for you.
+We just let it be here in case someone needs it in the future. 
+For people who doesn't know what the numbers mean, you can just remove these files from your local host.