Update src/Avalonia.Controls/Notifications/Notification.cs
Update src/Avalonia.Controls/Notifications/Notification.cs

improved xml comments

Co-Authored-By: Steven Kirk <ac6a5dd95d6e22de43a0511c4fb069330b6b03f0@users.noreply.github.com>
jkoritzinsky/Avalonia,SuperJMN/Avalonia,SuperJMN/Avalonia,SuperJMN/Avalonia,wieslawsoltes/Perspex,wieslawsoltes/Perspex,AvaloniaUI/Avalonia,AvaloniaUI/Avalonia,jkoritzinsky/Avalonia,jkoritzinsky/Avalonia,SuperJMN/Avalonia,AvaloniaUI/Avalonia,jkoritzinsky/Avalonia,jkoritzinsky/Perspex,AvaloniaUI/Avalonia,wieslawsoltes/Perspex,AvaloniaUI/Avalonia,jkoritzinsky/Avalonia,AvaloniaUI/Avalonia,grokys/Perspex,Perspex/Perspex,wieslawsoltes/Perspex,Perspex/Perspex,SuperJMN/Avalonia,wieslawsoltes/Perspex,wieslawsoltes/Perspex,AvaloniaUI/Avalonia,jkoritzinsky/Avalonia,wieslawsoltes/Perspex,akrisiun/Perspex,SuperJMN/Avalonia,SuperJMN/Avalonia,jkoritzinsky/Avalonia,grokys/Perspex