Update README.md

Added addHeader() description

Author: nullboundary

README.md

@@ -11,24 +11,30 @@ How to
 Install the library by [downloading the latest release](https://github.com/runemadsen/HTTProcessing/releases) or via the [Processing contribution manager](http://wiki.processing.org/w/How_to_Install_a_Contributed_Library).
 
 Then import the library in your sketch:
-    
-    import http.requests.*;
-
+```Java    
+import http.requests.*;
+```
 Then you can make GET and POST requests from your code:
-
-    GetRequest get = new GetRequest("http://httprocessing.heroku.com");
-    get.send();
-    println("Reponse Content: " + get.getContent());
-    println("Reponse Content-Length Header: " + get.getHeader("Content-Length"));
+```Java
+GetRequest get = new GetRequest("http://httprocessing.heroku.com");
+get.send();
+println("Reponse Content: " + get.getContent());
+println("Reponse Content-Length Header: " + get.getHeader("Content-Length"));
 
-    PostRequest post = new PostRequest("http://httprocessing.heroku.com");
-    post.addData("name", "Rune");
-    post.send();
-    println("Reponse Content: " + post.getContent());
-    println("Reponse Content-Length Header: " + post.getHeader("Content-Length"));
-
+PostRequest post = new PostRequest("http://httprocessing.heroku.com");
+post.addData("name", "Rune");
+post.send();
+println("Reponse Content: " + post.getContent());
+println("Reponse Content-Length Header: " + post.getHeader("Content-Length"));
+```
 To authenticate requests using a Basic Access authentication scheme, include the following in your requests:
-    
-    get.addUser("username", "password");
-
-    post.addUser("username", "password");
+```Java    
+get.addUser("username", "password");
+post.addUser("username", "password");
+```    
+ To add a header to your request, including the following:
+```Java 
+ //method: addHeader(name,value)
+ get.addHeader("Accept", "application/json");
+ post.addHeader("Content-Type", "application/json");
+```