Add Transfer-Encoding to the list of HTTP Headers

This closes #6

Signed-off-by: Alexander Shorin <kxepal@apache.org>

src/api/basics.rst

@@ -233,6 +233,19 @@ below.
    original ETag head (therefore sending back 304 Not Modified more
    often).
 
+-  ``Transfer-Encoding``
+
+   If the response uses an encoding, then it is specified in this
+   header field.
+
+   ``Transfer-Encoding: chunked`` means that the response is sent in
+   parts, a method known as `chunked transfer encoding`_. This is used
+   when CouchDB does not know beforehand the size of the data it will
+   send (for example, the :ref:`changes feed <changes>`).
+
+.. _chunked transfer encoding:
+   https://en.wikipedia.org/wiki/Chunked_transfer_encoding
+
 .. _json:
 
 JSON Basics