Update index.md

Author: zamronypj

docs/index.md

@@ -73,6 +73,8 @@ Open URL http://localhost/test.pas from Internet browser, you should see text `H
 
 If `test.pas` is downloaded then you do not register mod_pascal with Apache correctly.
 
+When not set, `Content-Type` response header is assumed `text/html`.
+
 To return response with header, add header line separated by newline
 
 ```
@@ -82,6 +84,15 @@ begin
     writeln('<h1>Hello from Pascal</h1>');
 end.
 ```
+or as JSON
+
+```
+begin
+    writeln('Content-Type : application/json');
+    writeln();
+    writeln('{"message":"Hello from Pascal"}');
+end.
+```
 
 Please note that because blank newline is used to mark end of header parts of response, for safety, always add them even if you do not want to set response header. For example