Add NTLM Authentication example to the README

CHANGES
========
- Add an example of NTLM authentication to the readme.

WHY
========
When searching for a solution to NTLM + Clojure all I found was the issues and
PRs for clj-http. It would have been great to see it somewhere in the docs so I
knew if it worked or not. Hopefully this will begin driving traffic to the
readme of this project rather than the issues and PRs.

Author: Joe Lane

README.org

@@ -41,6 +41,7 @@
 - [[#authentication][Authentication]]
   - [[#basic-auth][Basic Auth]]
   - [[#digest-auth][Digest Auth]]
+  - [[#ntlm-auth][NTLM Auth]]
   - [[#oauth2][oAuth2]]
 - [[#advanced-usage][Advanced Usage]]
   - [[#raw-request][Raw Request]]
@@ -860,6 +861,17 @@ There are four debugging methods you can use:
 
 #+END_SRC
 
+** NTLM Auth
+:PROPERTIES:
+:CUSTOM_ID: h:AE80FFDC-2016-4883-9512-2BE16640339D
+:END:
+
+#+BEGIN_SRC clojure
+
+(client/get "http://example.com/protected" {:ntlm-auth ["user" "pass" "host" "domain"]})
+
+#+END_SRC
+
 ** oAuth2
 :PROPERTIES:
 :CUSTOM_ID: h:dd077440-a1de-437e-b34e-5d6d0d1da4bd