nvmf: Update the getting started guide

/**

 * \page nvmf_getting_started NVMf Getting Started Guide

The NVMe over Fabrics target is a user space application that presents block devices over the

network using RDMA. It requires an RDMA-capable NIC with its corresponding OFED software package

installed to run. The target should work on all flavors of RDMA, but it is currently tested against

Mellanox NICs (RoCEv2) and Chelsio NICs (iWARP).

The NVMe over Fabrics specification defines subsystems that can be exported over the network. SPDK

has chosen to call the software that exports these subsystems a "target", which is the term used

for iSCSI. The specification refers to the "client" that connects to the target as a "host". Many

people will also refer to the host as an "initiator", which is the equivalent thing in iSCSI

parlance. SPDK will try to stick to the terms "target" and "host" to match the specification.

There will be both a target and a host implemented in the Linux kernel, and these are available

today as a set of patches against the kernel 4.8 release candidate. All of the testing against th

SPDK target has been against the proposed Linux kernel host. This means that for at least the host

machine, the kernel will need to be a release candidate until the code is actually merged. For the

system running the SPDK target, however, you can run any modern flavor of Linux as required by your

NIC vendor's OFED distribution.

\section nvmf_prereqs Prerequisites

To build nvmf there are some package dependencies.

This guide starts by assuming that you can already build the standard SPDK distribution on your

platform. By default, the NVMf target is not built. To build NVMf there are some additional

dependencies.

Fedora:

\verbatim

apt-get install libibverbs-dev librdmacm-dev

\endverbatim

Then build SPDK with the NVMf target enabled, either by editing CONFIG

to enable CONFIG_RDMA or enabling it on the `make` command line:

Then build SPDK with the NVMf target enabled, either by editing CONFIG to enable CONFIG_RDMA or

enabling it on the `make` command line:

\verbatim

make CONFIG_RDMA=y <other config parameters>

\endverbatim

Once built, the binary will be in `app/nvmf_tgt`.

\section nvmf_config Configuring NVMf

An NVMf specific configuration file is used to configure, or 'provision',

the NVMf target. This file defines the following:

 - general application parameters

 - global NVMf parameters

 - ports that define local RDMA interface ports the nvmf target will

     use for network access

 - initiator groups with names and addresses to allow access to nvmf target

     subsystems

 - list of NVMe HW device candidates to share via NVMf

 - NVMf target subsystem(s) that define the provision mappings between remote

     initiator groups and local target ports, and NVMe device

     namespaces

An example nvmf configuration file included with this package at

`etc/spdk/nvmf.conf.in`.

You must edit a version of this file for use in your environment and copy it

to /usr/local/etc/spdk/nvmf.conf.  Alternatively, you may also specify the

configuration file explicitly using `-c /path/to/nvmf.conf` when starting `nvmf_tgt`.

The `Port` and `Host` sections must be updated in all cases to

match the IP addresses in your network environment.

The `Nvme` section must also be updated with a the list of NVMe devices

that will be exported.  Each device is identified by a PCI bus, device, and function.

The NVMf target will display a list of NVMe devices discovered

in the system.  This information can then be used to select the list of devices

to populate this configuration file section.

An NVMf specific configuration file is used to configure, or 'provision', the NVMf target. This 

file's primary purpose is to define subsystems. A fully documented example configuration file is

located at `etc/spdk/nvmf.conf.in`.

You should make a copy of the example configuration file, modify it to suit your environment, and

then run the nvmf_tgt application and pass it the configuration file using the -c option. Right now,

the target requires elevated privileges (root) to run.

\verbatim

app/nvmf_tgt/nvmf_tgt -c /path/to/nvmf.conf

\endverbatim

*/