Add a bunch of doc comments

We get a lot of build output because of missing XML comments that we
ignore. I'd like to stop ignoring them. To do that, we need to doc the
💩 out of everything.

Octokit/Models/Request/NewRepositoryFork.cs

@@ -4,9 +4,22 @@ using System.Globalization;
 
 namespace Octokit
 {
+    /// <summary>
+    /// Used to fork a repository.
+    /// </summary>
+    /// <remarks>
+    /// API: https://developer.github.com/v3/repos/forks/#create-a-fork
+    /// </remarks>
     [DebuggerDisplay("{DebuggerDisplay,nq}")]
     public class NewRepositoryFork
     {
+        /// <summary>
+        /// Gets or sets the organization name to fork into (Optional). If not specified, creates a fork for the
+        /// authenticated user.
+        /// </summary>
+        /// <value>
+        /// The organization.
+        /// </value>
         public string Organization { get; set; }
 
         internal string DebuggerDisplay