Merge pull request #237 from accidentaldeveloper/patch-1

Update README.md to contain a warning, so that others do not make my mistake

README.md

@@ -250,7 +250,7 @@ public interface IGitHubApi
 #### Dynamic headers
 
 If the content of the header needs to be set at runtime, you can add a header
-with a dynamic  value to a request by applying a `Header` attribute to a parameter:
+with a dynamic value to a request by applying a `Header` attribute to a parameter:
 
 ```csharp
 [Get("/users/{user}")]
@@ -292,6 +292,8 @@ class AuthenticatedHttpClientHandler : HttpClientHandler
 }
 ```
 
+While HttpClient contains a nearly identical method signature, it is used differently. HttpClient.SendAsync is not called by Refit. The HttpClientHandler must be modified instead.
+
 This class is used like so (example uses the [ADAL](http://msdn.microsoft.com/en-us/library/azure/jj573266.aspx) library to manage auto-token refresh but the principal holds for Xamarin.Auth or any other library:
 
 ```csharp