Update page content on change event of file

I am developing a employee tracking app that keeps track of all employees that turn their pc on. To detect the pcs turning on, I developed a simple script with pyton and it works well It saves the employee is and time when he/she opened his/her computer in json format. However, I also have to develop a gui for the manager. Since I am not very advanced in using C#. I have decided on creating one webpage(plus using a webpage removes the need of any sort of installation) that shows who turned their computer on and off and when. The problem here is that I am not a web designer and I am at very basic level at php and js. I can read from files and decode json. I managed to update the page when the user reloads it. However, it should automatically update itself and the php code only runs when the client reloads the page.

So here is my actual question, how can I constantly check for changes in a file and upload the page content accordingly.

Sorry I couldn't post the code. I am currently travelling and my laptop isn't with me.