style: Add XML comments to missing members

Author: DevD4v3

src/Attributes/PluginAttribute.cs

@@ -4,6 +4,8 @@ namespace CPlugin.Net;
 
 /// <summary>
 /// This attribute is required so that the plugin loader can create the instance of the type that implements the contract.
+/// <para>Example:</para>
+/// <c>[assembly: Plugin(typeof(PluginStartup))]</c>
 /// </summary>
 [AttributeUsage(AttributeTargets.Assembly, Inherited = false, AllowMultiple = true)]
 public class PluginAttribute : Attribute

src/Core/Configuration/CPluginJsonConfiguration.cs

@@ -22,6 +22,9 @@ public class CPluginJsonConfiguration : CPluginConfigurationBase
     /// <summary>
     /// Initializes a new instance of the <see cref="CPluginJsonConfiguration"/> class.
     /// </summary>
+    /// <param name="configuration">
+    /// A set of key/value application configuration properties.
+    /// </param>
     /// <exception cref="ArgumentNullException">
     /// <c>configuration</c> is <c>null</c>.
     /// </exception>

src/Core/PluginLoader.cs

@@ -50,6 +50,9 @@ public static void SetConfiguration(CPluginConfigurationBase configuration)
     /// An instance of type <see cref="IEnumerable{TContract}"/> that contains the instances
     /// that implement the contract specified by <typeparamref name="TContract"/>.
     /// </returns>
+    /// <exception cref="InvalidOperationException">
+    /// If a plugin does not use the <see cref="PluginAttribute"/> type at the assembly level.
+    /// </exception>
     public static IEnumerable<TContract> Load<TContract>() where TContract : class
     {
         var contracts = new List<TContract>();