Problem: design goals and supported platforms are not explicitly stated

Solution: add section on design goals and supported platforms to README, improve overall structure of README

Author: sigiesec

README.md

@@ -1,7 +1,50 @@
-This is C++ binding for 0MQ
+[![Travis-CI Status](https://travis-ci.org/zeromq/cppzmq.svg?branch=master)](https://travis-ci.org/zeromq/cppzmq)
+[![Appveyor Status](https://ci.appveyor.com/api/projects/status/bvi5axi8um7goh50/branch/master?svg=true)](https://ci.appveyor.com/project/zeromq/cppzmq/branch/master)
+[![Coverage Status](https://coveralls.io/repos/github/zeromq/cppzmq/badge.svg?branch=master)](https://coveralls.io/github/zeromq/cppzmq?branch=master)
+
+Introduction & Design Goals
+===========================
+
+cppzmq is a C++ binding for libzmq. It has the following design goals:
+ - cppzmq maps the libzmq C API to C++ concepts. In particular:
+   - it is type-safe (the libzmq C API exposes various class-like concepts as void*)
+   - it provides exception-based error handling (the libzmq C API provides errno-based error handling)
+   - it provides RAII-style classes that automate resource management (the libzmq C API requires the user to take care to free resources explicitly)
+ - cppzmq is a light-weight, header-only binding. You only need to include the header file zmq.hpp (and maybe zmq_addon.hpp) to use it.
+ - zmq.hpp is meant to contain direct mappings of the abstractions provided by the libzmq C API, while zmq_addon.hpp provides additional higher-level abstractions.
+
+There are other C++ bindings for ZeroMQ with different design goals. In particular, none of the following bindings are header-only:
+ - [zmqpp](https://github.com/zeromq/zmqpp) is a high-level binding to libzmq.
+ - [czmqpp](https://github.com/zeromq/czmqpp) is a binding based on the high-level czmq API.
+ - [fbzmq](https://github.com/facebook/fbzmq) is a binding that integrates with Apache Thrift and provides higher-level abstractions in addition. It requires C++14.
+
+Supported platforms
+===================
+
+ - Only a subset of the platforms that are supported by libzmq itself are supported. Some features already require a compiler supporting C++11. In the future, probably all features will require C++11. To build and run the tests, cmake and googletest are required.
+ - Tested libzmq versions are
+   - 4.2.0 (without DRAFT API)
+   - 4.2.5 (with and without DRAFT API)
+ - Platforms with full support (i.e. CI executing build and tests)
+   - Ubuntu 14.04 x64 (with gcc 4.8.4) (without DRAFT API only)
+   - Ubuntu 14.04 x64 (with gcc 7.3.0)
+   - Visual Studio 2015 x86
+   - Visual Studio 2017 x86
+ - Additional platforms that are known to work:
+   - We have no current reports on additional platforms that are known to work yet. Please add your platform here. If CI can be provided for them with a cloud-based CI service working with GitHub, you are invited to add CI, and make it possible to be included in the list above.
+ - Additional platforms that probably work:
+   - Any platform supported by libzmq that provides a sufficiently recent gcc (4.8.1 or newer) or clang (3.3 or newer)
+   - MacOS X
+   - Visual Studio 2012+ x86/x64
+
+Contribution policy
+===================
 
 The contribution policy is at: http://rfc.zeromq.org/spec:22
 
+Build instructions
+==================
+
 Build steps:
 
 1. Build [libzmq](https://github.com/zeromq/libzmq) via cmake. This does an out of source build and installs the build files