add summary comment.

src/DotNetCore.CAP/ICapOptionsExtension.cs

@@ -2,8 +2,15 @@
 
 namespace DotNetCore.CAP
 {
+    /// <summary>
+    /// Cap options extension
+    /// </summary>
     public interface ICapOptionsExtension
     {
+        /// <summary>
+        /// Registered child service.
+        /// </summary>
+        /// <param name="services">add service to the <see cref="IServiceCollection"/></param>
         void AddServices(IServiceCollection services);
     }
 }
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