desktop: add auto update url

desktop/src/index.ts

-import { app, BrowserWindow, ipcMain, dialog } from 'electron'
+import { app, BrowserWindow, autoUpdater } from 'electron'
 import { spawn } from 'child_process'
 import * as path from 'path'
 
@@ -82,3 +82,4 @@ app.on('activate', () => {
 
 // In this file you can include the rest of your app's specific main process
 // code. You can also put them in separate files and import them here.
+autoUpdater.setFeedURL({ url: `https://updates.ollama.ai/update/${process.platform}/${app.getVersion()}` })