Update documents

Author: methane

README.rst

@@ -59,7 +59,7 @@ Package is uploaded on `PyPI <https://pypi.org/project/PyMySQL>`_.
 
 You can install it with pip::
 
-    $ pip3 install PyMySQL
+    $ python3 -m pip install PyMySQL
 
 
 Documentation

docs/source/user/installation.rst

@@ -6,24 +6,22 @@ Installation
 
 The last stable release is available on PyPI and can be installed with ``pip``::
 
-    $ pip install PyMySQL
+    $ python3 -m pip install PyMySQL
 
 Requirements
 -------------
 
 * Python -- one of the following:
 
-  - CPython_ >= 2.6 or >= 3.3
-  - PyPy_ >= 4.0
-  - IronPython_ 2.7
+  - CPython_ >= 2.7 or >= 3.4
+  - Latest PyPy_
 
 * MySQL Server -- one of the following:
 
-  - MySQL_ >= 4.1  (tested with only 5.5~)
-  - MariaDB_ >= 5.1
+  - MySQL_ >= 5.5
+  - MariaDB_ >= 5.5
 
 .. _CPython: http://www.python.org/
 .. _PyPy: http://pypy.org/
-.. _IronPython: http://ironpython.net/
 .. _MySQL: http://www.mysql.com/
 .. _MariaDB: https://mariadb.org/