update docs day 1

Author: tamht298

day-1/bg-day02.png renamed to day-1/bg-day01.png

@@ -81,4 +81,4 @@ Link reference post: [here](https://facebook.com/groups/AngularVietnam/permalink
 [eslint-url]: https://marketplace.visualstudio.com/items?itemName=dbaeumer.vscode-eslint
 [nxconsole-url]: https://marketplace.visualstudio.com/items?itemName=nrwl.angular-console
 [group-fb-url]: https://www.facebook.com/groups/AngularVietnam
-[bg-url]: https://github.com/tamht298/100DaysOfCodeAngular/blob/master/day-1/day-1.png
+[bg-url]: https://github.com/tamht298/100DaysOfCodeAngular/blob/d-1/day-1/bg-day01.png