Update README.md

SharepointToolbox/Services/ProfileService.cs

@@ -24,8 +24,9 @@ public class ProfileService
             !Uri.TryCreate(profile.TenantUrl, UriKind.Absolute, out _))
             throw new ArgumentException("TenantUrl must be a valid absolute URL.", nameof(profile));
 
-        if (string.IsNullOrWhiteSpace(profile.ClientId))
-            throw new ArgumentException("ClientId must not be empty.", nameof(profile));
+        // ClientId is optional at creation time: the user can register the app from within
+        // the tool, which will populate ClientId/AppId on the profile afterwards.
+        profile.ClientId ??= string.Empty;
 
         var existing = (await _repository.LoadAsync()).ToList();
         existing.Add(profile);