Add a dev oauth app config similar to how desktop does it

(https://github.com/desktop/desktop/blob/master/docs/technical/oauth.md)

Author: shana

src/GitHub.Api/Application/ApplicationInfo.cs

@@ -14,8 +14,24 @@ static partial class ApplicationInfo
 #endif
         public const string ApplicationDescription = "GitHub for Unity";
 
+#if DEBUG
+/*
+        For external contributors, we have bundled a developer OAuth application
+        called `GitHub for Unity (dev)` so that you can complete the sign in flow
+        locally without needing to configure your own application.
+        This is for testing only and it is (obviously) public, proceed with caution.
+
+        For a release build, you should create a new oauth application on github.com,
+        copy the `common/ApplicationInfo_Local.cs-example`
+        template to `common/ApplicationInfo_Local.cs` and fill out the `myClientId` and
+        `myClientSecret` fields for your oauth app.
+ */
+        internal static string ClientId { get; private set; } = "924a97f36926f535e72c";
+        internal static string ClientSecret { get; private set; } = "b4fa550b7f8e38034c6b1339084fa125eebb6155";
+#else
         internal static string ClientId { get; private set; } = "";
         internal static string ClientSecret { get; private set; } = "";
+#endif
 
         public static string Version { get { return System.AssemblyVersionInformation.Version; } }