Add some examples

Note that the example on redirecting a URL is BROKEN.  Possibly a bug in Kapow!

doc/writing_headers.rst

@@ -0,0 +1,18 @@
+Writing Headers
+===============
+
+The HTTP protocol allows metadata using headers.
+
+Kapow! allows you to set them easily:
+
+
+In this example, we respond by setting the ``Content-Type`` header
+to the value ``application/json``.
+.. code-block:: bash
+
+   kapow set /response/headers/Content-Type application/json
+
+We could then return some JSON content:
+.. code-block:: bash
+
+   echo '{"data": "some relevant string"}' | kapow set /response/body