[Docs restructuring]Introduction to Fuel

Rewrote the Fuel introduction section.
Added the Introduction to Fuel installation section.

Change-Id: I2f371300869078fc2d344c4bedca0a6cced2f80b
Partial-Bug: #1504699

pages/draft/fuel-install-guide/intro_fuel_install_intro.rst

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+.. _intro_fuel_install:
+
+=====================================
+Introduction to the Fuel Installation
+=====================================
+
+This section provides an overview of the Fuel installation
+process. You can install Fuel on a server with an Internet connection or
+on a server that is isolated from the Internet for security reasons. Depending
+on your choice, the workflow differs.
+
+This section includes the following topics:
+
+* : ref :intro_fuel
+* : ref :intro_install_overview
+* : ref :intro_planning
+
+
+
+

pages/draft/fuel-install-guide/intro_fuel_intro.rst

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+.. _intro_fuel:
+
+Introduction to Fuel
+~~~~~~~~~~~~~~~~~~~~
+
+Fuel is an open-source software application that simplifies the deployment of
+highly available OpenStack environments, as well as enables you to
+manage your OpenStack environments after deployment.
+
+Fuel provides a web user interface (WUI), as well as a command-line user
+interface (CLI) and RESTful API for provisioning, configuration, and
+management of OpenStack environments. A link to the Horizon OpenStack
+Dashboard appears in the Fuel web UI after you deploy an OpenStack
+environment.
+
+Using Fuel you can:
+
+- Deploy multiple highly-available OpenStack environments on virtual or bare
+  metal hardware.
+
+- Configure and verify network configurations.
+
+- Test interoperability between the OpenStack components.
+
+- Easily scale your OpenStack environment by adding and removing nodes.
+
+Fuel architecture includes:
+
+* Fuel Master node
+  A server with the installed Fuel application that performs initial
+  configuration, provisioning, and PXE booting of the Fuel Slave nodes, as
+  well as assigning the IP addresses to the Fuel Slave nodes.
+
+* Fuel Slave node
+  In the Fuel project terminology, a generic term that describes a server that
+  is provisioned by the Fuel Master node. A Fuel Slave node can be a
+  controller, compute, or storage node, among others. These terms are
+  interchangeable with the OpenStack terminology.
+
+.. seealso::
+
+   - `Fuel Architecture
+     <https://docs.fuel-infra.org/fuel-dev/develop/architecture.html>`_