doc: add basic documentation (#23)

Author: spy16

docs/glossary.md

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+# Glossary
+
+This section describes the core elements of dex.

docs/installation.md

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+# Installation
+
+Dex ships as a single binary without any external dependencies making the installation very simple.
+
+Dex is available for all major platforms (e.g., macOS, Windows, Linux, OpenBSD, FreeBSD, etc.)
+
+Approaches to install Dex:
+
+1. Using a [pre-compiled binary](#binary-cross-platform)
+2. Installing with [package manager](#homebrew)
+3. Installing from [source](#building-from-source)
+4. Installing with [Docker](#using-docker-image)
+
+## Binary (Cross-platform)
+
+Download the appropriate version for your platform from [releases](https://github.com/odpf/dex/releases) page. Once
+downloaded, the binary can be run from anywhere. You don’t need to install it into a global location. This works well
+for shared hosts and other systems where you don’t have a privileged account. Ideally, you should install it somewhere
+in your PATH for easy use. `/usr/local/bin` is the most probable location.
+
+## Homebrew
+
+```sh
+# Install dex (requires homebrew installed)
+brew install odpf/taps/dex
+
+# Upgrade dex (requires homebrew installed)
+brew upgrade dex
+
+# Check for installed dex version
+dex version
+```
+
+## Building from source
+
+To compile from source, you will need [Go](https://golang.org/) installed in your `PATH`.
+
+```bash
+# Clone the repo
+https://github.com/odpf/dex.git
+
+# Build dex binary file
+make build
+
+# Check for installed dex version
+./dex version
+```
+
+## Using Docker image
+
+Dex ships a Docker image [odpf/dex](https://hub.docker.com/r/odpf/dex) that enables you to use `dex` as part of your Docker workflow.
+
+For example, you can run `dex version` with this command:
+
+```bash
+docker run odpf/dex version
+```

docs/introduction.md

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+# Introduction
+
+Welcome to intro guide to Dex! This guide is the best place to start with Dex. We cover what Dex is, what problems it can solve, how it compares to existing DevOps practices, and how you can get started using it.
+
+## What is Dex?
+
+Dex is a platform that integrates all ODPF tools to provide a great experience for ODPF users.
+
+## Why is dex required?
+
+ODPF offers a suite of different data engineering tools. Each tool is designed with a specific use-case in mind and usually easy to setup. But in a real world setup, a lot of the tools also need to be configured & integrated to work together to get the most out of them.
+
+Dex is being developed to reduce the support effort that goes into provisioning, integrating and scaling of these tools.
+
+Dex will use [Entropy](https://github.com/odpf/entropy) to provision and manage deployments of various ODPF tools.

docs/usage_server.md

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+# Usage as Server
+
+The following sections will detail the steps necessary to run the Dex server.
+
+> Note: For installation instructions, refer [Installation](./installation.md) page.
+
+## Pre-requisites
+
+Dex is stateless and as such has no requirement of stateful components like databases, cache, etc.
+
+But Dex is an orchestrator and needs the following ODPF services:
+
+1. [Entropy](https://github.com/odpf/entropy) - Used for deployment and management of applications (e.g., firehose)
+2. [Siren](https://github.com/odpf/siren) - Used for configuring and managing alerting for tools deployed using Dex.
+3. [Shield](https://github.com/odpf/shield) - Used for access-control and project level metadata.
+
+## Configurations
+
+All the supported server configurations are documented in the [dex_server.yml](../dex_server.yml) file that is also shipped with the release package.
+
+This configuration file comes with sensible defaults wherever possible.
+
+## Running
+
+Once you tune the configuration file as needed, dex server can be started by running the following command:
+
+```shell
+dex server start --config dex_server.yml
+```