API interface summaries

Modified existing comments in IGitDatabaseClient, IMiscellaneousClient and
ITeamsClient. Hopefully for valid reasons.

Octokit/Clients/IGitDatabaseClient.cs

@@ -1,8 +1,11 @@
 namespace Octokit
 {
     /// <summary>
-    /// Used to maintain api structure therefore contains no methods
+    /// A client for GitHub's Git API.
     /// </summary>
+    /// <remarks>
+    /// See the <a href="http://developer.github.com/v3/git/">Git API documentation</a> for more information.
+    /// </remarks>
     public interface IGitDatabaseClient
     {
         IBlobsClient Blob { get; set; }