Document that 'params' can also be a list of tuples

Like we just did for 'data', 'params' follows the same processing and
can also be a list of tuples.

requests/api.py

@@ -18,7 +18,8 @@ def request(method, url, **kwargs):
 
     :param method: method for the new :class:`Request` object.
     :param url: URL for the new :class:`Request` object.
-    :param params: (optional) Dictionary or bytes to be sent in the query string for the :class:`Request`.
+    :param params: (optional) Dictionary, list of tuples or bytes to send
+        in the body of the :class:`Request`.
     :param data: (optional) Dictionary, list of tuples, bytes, or file-like
         object to send in the body of the :class:`Request`.
     :param json: (optional) A JSON serializable Python object to send in the body of the :class:`Request`.
@@ -63,7 +64,8 @@ def get(url, params=None, **kwargs):
     r"""Sends a GET request.
 
     :param url: URL for the new :class:`Request` object.
-    :param params: (optional) Dictionary or bytes to be sent in the query string for the :class:`Request`.
+    :param params: (optional) Dictionary, list of tuples or bytes to send
+        in the body of the :class:`Request`.
     :param \*\*kwargs: Optional arguments that ``request`` takes.
     :return: :class:`Response <Response>` object
     :rtype: requests.Response

requests/models.py

@@ -208,7 +208,9 @@ class Request(RequestHooksMixin):
         list of tuples ``[(key, value)]`` is provided, form-encoding will
         take place.
     :param json: json for the body to attach to the request (if files or data is not specified).
-    :param params: dictionary of URL parameters to append to the URL.
+    :param params: URL parameters to append to the URL. If a dictionary or
+        list of tuples ``[(key, value)]`` is provided, form-encoding will
+        take place.
     :param auth: Auth handler or (user, pass) tuple.
     :param cookies: dictionary or CookieJar of cookies to attach to this request.
     :param hooks: dictionary of callback hooks, for internal usage.