Tweak docs about older versions of 3.3 not tested or working with SSL.

Fixes #856

[skip ci]

README.rst

@@ -27,7 +27,7 @@ Check out the detailed changelog_ for this version.
 Get gevent
 ==========
 
-Gevent runs on Python >= 2.7, Python >= 3.3, or PyPy >= 4.0.1
+Gevent runs on Python >= 2.7, Python >= 3.3.5, or PyPy >= 4.0.1
 (but not PyPy3) (*Note*: PyPy is not supported in Windows). On all
 platforms, installing setuptools is recommended (this is done
 automatically if working in a virtual environment).

doc/intro.rst

@@ -28,6 +28,12 @@ supported. (Users of older versions of Python 2 need to install gevent
 1.0.x (2.5) or 1.1.x (2.6); Python 3 is not supported by 1.0.) gevent requires the
 greenlet__ library.
 
+.. note:: For Python 3.3, version 3.3.5 or newer is required to use
+          the gevent's SSL support due to bugs in the standard library of older
+          versions. For Python 2, 2.7.9 or newer is recommended for
+          the best SSL support; 2.7.8 is also tested although it
+          offers a less-secure SSL module.
+
 gevent 1.1 also runs on PyPy 2.6.1 and above, although 5.0 or above is
 strongly recommended. On PyPy, there are no external dependencies.