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/SearchQualifierOperator.cs

@@ -1,10 +1,28 @@
 namespace Octokit
 {
+    /// <summary>
+    /// Used to qualify a serch term.
+    /// </summary>
     public enum SearchQualifierOperator
     {
-        GreaterThan, // >
-        LessThan, // <
-        LessThanOrEqualTo, // <=
-        GreaterThanOrEqualTo// >=
+        /// <summary>
+        /// Greater than "&gt;"
+        /// </summary>
+        GreaterThan,
+
+        /// <summary>
+        /// Less than "&lt;"
+        /// </summary>
+        LessThan,
+
+        /// <summary>
+        /// Less than or equal to. "&lt;="
+        /// </summary>
+        LessThanOrEqualTo,
+
+        /// <summary>
+        /// Greater than or equal to. "&gt;="
+        /// </summary>
+        GreaterThanOrEqualTo
     }
 }