Electron - fix missing underline (#522)

Author: Mohammad Hunan Chughtai

source/node/electron.txt

@@ -56,7 +56,7 @@ To set up a React application with {+service+} using Electron use the following
 .. include:: /includes/steps/realm-with-electron-using-create-react-app.rst
 
 Working with Realm Using Renderer and Main Processes
------------------------------------------------
+----------------------------------------------------
 
 Electron applications have one main process. The main process can create
 multiple BrowserWindows. Each BrowserWindow spawns its own process.