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/NewDeployKey.cs

@@ -7,11 +7,26 @@ namespace Octokit
     /// <summary>
     /// Describes a new deployment key to create.
     /// </summary>
+    /// <remarks>
+    /// API: https://developer.github.com/v3/repos/keys/
+    /// </remarks>
     [DebuggerDisplay("{DebuggerDisplay,nq}")]
     public class NewDeployKey
     {
+        /// <summary>
+        /// Gets or sets a name for the deployment key.
+        /// </summary>
+        /// <value>
+        /// The title.
+        /// </value>
         public string Title { get; set; }
 
+        /// <summary>
+        /// Gets or sets the contents of the deployment key.
+        /// </summary>
+        /// <value>
+        /// The key.
+        /// </value>
         public string Key { get; set; }
 
         /// <summary>