Add return type on cookies.py

http://docs.python-requests.org/en/master/api/#api-cookies

requests/cookies.py

@@ -511,6 +511,7 @@ def cookiejar_from_dict(cookie_dict, cookiejar=None, overwrite=True):
     :param cookiejar: (optional) A cookiejar to add the cookies to.
     :param overwrite: (optional) If False, will not replace cookies
         already in the jar with new ones.
+    :rtype: CookieJar
     """
     if cookiejar is None:
         cookiejar = RequestsCookieJar()
@@ -529,6 +530,7 @@ def merge_cookies(cookiejar, cookies):
 
     :param cookiejar: CookieJar object to add the cookies to.
     :param cookies: Dictionary or CookieJar object to be added.
+    :rtype: CookieJar
     """
     if not isinstance(cookiejar, cookielib.CookieJar):
         raise ValueError('You can only merge into CookieJar')