Rewrite some text on the home page, and add a mention of iperf2.

That mention points to the iperf3 FAQ, which contains information
about the history of iperf2 and iperf3, and a pointer to continued
iperf2 development.  Suggested by a comment from @beau-williamson
in #27.

docs/faq.rst

@@ -1,3 +1,5 @@
+.. _faq:
+
 iperf3 FAQ
 ==========
 

docs/index.rst

@@ -6,10 +6,11 @@
 iperf3
 ======
 
-iperf is a tool for active measurements of the maximum achievable
-bandwidth on IP networks.  It supports tuning of various parameters
-related to timing, protocols, and buffers.  For each test it reports
-the measured throughput, loss, and other parameters.
+The iperf series of tools perform active measurements to determine the
+maximum achievable bandwidth on IP networks.  It supports tuning of
+various parameters related to timing, protocols, and buffers.  For
+each test it reports the measured throughput, loss, and other
+parameters.
 
 This version, sometimes referred to as iperf3, is a redesign of an
 original version developed at NLANR / DAST.  iperf3 is a new
@@ -30,6 +31,12 @@ iperf3 is principally developed by `ESnet <http://www.es.net/>`_ /
 `Lawrence Berkeley National Laboratory <http://www.lbl.gov/>`_.  It
 is released under a three-clause BSD license.
 
+iperf2 is no longer being developed by its original maintainers.
+However, beginning in 2014, another developer began fixing bugs and
+enhancing functionality, and generating releases of iperf2.  Both
+projects (as of late 2017) are currently being developed actively, but
+independently.  More information can be found in the :ref:`faq`.
+
 Links for the Impatient
 -----------------------