message: added doc for dataman
diff: DataMan for WAN
  ***************
  -Coming soon...
  +The DataMan engine is designed for data transfers over the wide area network. To use this engine, you can either specify it in your xml config file, with tag ``<engine type=DataMan>`` or set it in your application code:
  +
  +.. code-block:: c++
  +
  + adios2::IO datamanIO = adios.DeclareIO("ioName");
  + datamanIO.SetEngine("DataMan");
  + adios2::Engine datamanReader = datamanIO.Open(filename, adios2::Mode::Write);
  +
  +On the reader side you need to do instead:
  +
  +.. code-block:: c++
  +
  + adios2::IO datamanIO = adios.DeclareIO("ioName");
  + datamanIO.SetEngine("DataMan");
  + adios2::Engine datamanReader = datamanIO.Open(filename, adios2::Mode::Read);
  +
  +The DataMan engine does not accept any parameters. However, users are allowed to specify the following transport parameters:
  +
  +1. **Library**: the underlying network / socket library used for data transfer.
  +
  +2. **IPAddress**: the IP address of the host where the writer application runs.
  +
  +3. **Port**: the port on the writer host that will be used for data transfers.
  +
  +4. **Timeout**: the timeout in seconds to wait for every send / receive.
  +
  +============= ================= ================================================
  + **Key** **Value Format** **Default** and Examples
  +============= ================= ================================================
  + Library string **ZMQ**
  + IPAddress string **127.0.0.1**, 22.195.18.29
  + Port integer **12306**, 22000, 33000
  + Timeout integer **5**, 10, 30
  +============= ================= ================================================
  +
  +
  