Update README-en.md

Author: iKineticate

README-en.md

@@ -10,7 +10,7 @@ A lightweight tray tool for easily checking the battery level of your Bluetooth
 - [x] Setting：Bluetooth Device power as tray icon  
     Support custom icons:   
         (1) open tray menu -- `Settings` -- `Open Config` -- `font_name = "System Font Nmae"` + `font_color = "Hex color code，e.g. #FFFFFF、#00D26A"`,  restart BlueGauge after setting   
-        (2) create an assets folder in the software directory, and then add 0.png to 100.png pictures.  
+        (2) create an assets folder in the software directory, and then add `0.png` to `100.png` pictures.  
     ![image](screenshots/battery.png)
 - [x] Setting：Auto start
 - [x] Setting：Update interval