Update README
Add warning about pip version.
@@ -55,8 +55,15 @@ Same as usual, it can be installed with `pip`
.. code-block:: bash
+ $ pip install -U pip
$ pip install aqtinstall
+You are recommended to update pip before installing aqtinstall.
+aqtinstall depends several packages, that is required to extract 7zip archives,
+some of which are precompiled in several platforms.
+Older pip does not handle it expectedly.(see #230)
+
+
Usage
-----
