Update

README.md

 
 The web interface itself uses [Plotly.js](https://plot.ly/javascript/) to display the histogram of the channels in realtime by connecting to the websocket endpoint and provides a convenient user interface for exploring the details of the gamma-spectrum.
 
-![Background Gamma Spectrum](docs/background-gamma-spectrum.png)
+![Background Gamma Spectrum](docs/background-gamma-spectrum.white.png)