Add Sparkle update path

- Invoke `checkForUpdatesInBackground` when the user runs the app
- Add `SUFeedURL` to the `Info.plist`
- Add `appcast.xml` file

App/Resources/Info.plist

@@ -36,6 +36,8 @@
 	<true/>
 	<key>com.apple.security.automation.apple-events</key>
 	<true/>
+  <key>SUFeedURL</key>
+  <string>https://raw.githubusercontent.com/zenangst/KeyboardCowboy/master/appcast.xml</string>
 	<key>SUPublicEDKey</key>
 	<string>ZxEpbxbd8TIwNev9bkzaLrHAaQUK/x0wBTHb4anScsc=</string>
 </dict>

App/Sources/Application/Saloon.swift

@@ -5,6 +5,7 @@ import LogicFramework
 import ModelKit
 import ViewKit
 import SwiftUI
+import Sparkle
 
 /*
  This type alias exists soley to restore some order to all the chaos.
@@ -102,6 +103,8 @@ class Saloon: ViewKitStore, MenubarControllerDelegate {
     subscribe(to: UserDefaults.standard, context: context)
     subscribe(to: NotificationCenter.default)
     loaded = true
+
+    SUUpdater.shared()?.checkForUpdatesInBackground()
   }
 
   func receive(_ scenePhase: ScenePhase) {

appcast.xml

@@ -0,0 +1,12 @@
+<?xml version="1.0" standalone="yes"?>
+<rss xmlns:sparkle="http://www.andymatuschak.org/xml-namespaces/sparkle" version="2.0">
+    <channel>
+        <title>Keyboard Cowboy</title>
+        <item>
+            <title>0.4.1</title>
+            <pubDate>Sun, 20 Dec 2020 19:50:28 +0100</pubDate>
+            <sparkle:minimumSystemVersion>11.0</sparkle:minimumSystemVersion>
+            <enclosure url="Keyboard_Cowboy_0.4.1.zip" sparkle:version="18" sparkle:shortVersionString="0.4.1" length="2871926" type="application/octet-stream"/>
+        </item>
+    </channel>
+</rss>