Explain the observed slowness of bench_sendall under PyPy and link to the...

Explain the observed slowness of bench_sendall under PyPy and link to the discussion on the PyPy issue tracker. [skip ci]

README.rst

@@ -24,7 +24,8 @@ gevent_ is written and maintained by `Denis Bilenko`_ and is licensed under MIT
 get gevent
 ==========
 
-Install Python 2.6, 2.7, 3.3 or 3.4 and greenlet_ extension.
+Install Python 2.6, 2.7, 3.3 or 3.4 along with the greenlet_
+extension. Or install PyPy 2.6 or above (but not PyPy3).
 
 Download the latest release from `Python Package Index`_ or clone `the repository`_.
 

doc/whatsnew_1_1.rst

@@ -17,6 +17,28 @@ Support for Python 2.5 was removed when support for Python 3 was
 added. Any further releases in the 1.0.x line will maintain support
 for Python 2.5.
 
+PyPy Notes
+----------
+
+PyPy has been tested on OS X and 64-bit Linux from version 2.5.0
+through 2.5.1, 2.6.0 and pre-release versions of 2.7.0.
+
+- Version 2.7.0 is required for the most robust signal handling. Prior
+  to 2.7.0, signals could be delivered incorrectly or fail to be
+  delivered during a blocking operation.
+- Overall performance seems to be quite acceptable with newer versions
+  of PyPy. Things that are known or expected to be slower under PyPy
+  include the :mod:`c-ares resolver <gevent.resolver_ares>` and
+  :meth:`socket.socket.sendall`. In particular,
+  :meth:`socket.socket.sendall` can be `relatively slow`_ for large
+  transmissions. This can be mitigated by setting a larger write
+  buffer on the socket, e.g, ``sock.setsockopt(socket.SOL_SOCKET,
+  socket.SO_SNDBUF, 1024*1024)`` Whether or not these matter will
+  depend on the workload of each application.
+
+.. _relatively slow: https://bitbucket.org/pypy/pypy/issues/2091/non-blocking-socketsend-slow-gevent
+
+
 Improved subprocess support
 ===========================