Update README to describe peadm module better

The README should give readers a better sense of what the peadm module
is, what it does, what it affects, and what it does not affect. This
commit provides an incremental improvement towards that end.

Author: reidmv

CHANGELOG.md

@@ -1,7 +1,13 @@
 # PEADM module
 
 ## Unreleased
-- add service module as a dependency
+### Summary
+
+Documentation and README update
+
+### Improvements
+
+- Provide a useful overview of the module in the README so that readers can quickly gain a sense of how the module is used, what it affects, and what it does not affect.
 
 ## Release 2.1.1
 ### Summary

README.md

@@ -1,38 +1,69 @@
 # Puppet Enterprise (pe) Administration (adm) Module
 
-This Puppet module contains Bolt plans used to deploy and manage Puppet Enterprise infrastructure. Plans are provided to automate common lifecycle activities, in order to increase velocity and reduce the possibility of human error incurred by manually performing these activities.
+This Puppet module contains Bolt plans used to deploy and manage Puppet Enterprise infrastructure. Plans are provided to automate common lifecycle activities in order to increase velocity and reduce the possibility of human error incurred by manually performing these activities.
 
 The peadm module is able to deploy and manage Puppet Enterprise 2019.x Standard, Large, and Extra Large architectures.
 
+#### Table of Contents
+
+1. [Expectations](#expectations)
+1. [Overview](#overview)
+    * [What peadm affects](#what-peadm-affects)
+    * [What peadm does not affect](#what-peadm-does-not-affect)
+    * [Requirements](#requirements)
+3. [Usage](#usage)
+4. [Reference](#reference)
+5. [Getting Help](#getting-help)
+
 ## Expectations
 
 The peadm module is intended to be used only by Puppet Enterprise customers actively working with and being guided by Puppet Customer Success teams—specifically, the Professional Services and Solutions Architecture teams. Independent use is not recommended for production environments without a comprehensive understanding of the peadm module.
 
-## Documentation
+## Overview
+
+The normal usage pattern for peadm is as follows.
+
+1. Users set up a Bolt host from which they can run peadm plans. The Bolt host can be any machine that has ssh access to all of the PE nodes.
+2. Users run the `peadm::provision` plan to bootstrap a new PE deployment. Depending on the architecture chosen, peadm may create some node groups in the classifier to set parameters on the built-in `puppet_enterprise` module, tuning it for large or extra large architectures.
+3. Users use and operate their PE deployment as normal. The peadm module is not used again until the next upgrade.
+4. When it is time to upgrade, users run the `peadm::upgrade` plan from their Bolt host to accelerate and aid in the upgrade process.
+
+### What peadm affects
+
+* The `peadm::provision` plan adds a number of custom OID trusted facts to the certificates of PE infrastructure nodes as it deploys them. These trusted facts are later used by the plans to quickly and correctly identify nodes in particular roles.
+* Up to four node groups may be created to help configure `puppet_enterprise` class parameters for PE infrastructure roles. The most notable configuration is the designation of compilers as being either "A" or "B" nodes for availability.
+
+### What peadm does not affect
 
-See this README file and any documents in the [documentation](documentation) directory.
+* The peadm module is not required to exist or be present outside of the point(s) in time it is used to create a new PE deployment, or upgrade an existing deployment. No new Puppet classes or other persistent content not provided out-of-box by PE itself is applied to PE infrastructure nodes by the peadm module.
+* Having used the peadm module to provision or to upgrade a PE deployment is not known to affect or curtail the ability to use any normal, documented PE procedures, e.g. failover to a replica, or manual upgrade of a deployment.
 
-Plans:
+### Requirements
+
+* Puppet Enterprise 2019.8.1 or newer (tested with PE 2019.8.1)
+* Bolt 2.27.0 or newer (tested with Bolt 2.27.0)
+* EL 7, EL 8, Ubuntu 18.04, or Ubuntu 20.04
+* Classifier Data enabled. This PE feature is enabled by default on new installs, but can be disabled by users if they remove the relevant configuration from their global hiera.yaml file. See the [PE docs](https://puppet.com/docs/pe/latest/config_console.html#task-5039) for more information.
+
+## Usage
+
+Follow the links below to usage instructions for each peadm plan.
 
 * [Provision](documentation/provision.md)
 * [Upgrade](documentation/upgrade.md)
 * [Convert](documentation/convert.md)
 * [Status](documentation/status.md)
 
-Reference:
+## Reference
+
+Additional documentation and information pertaining to various aspects or elements of peadm.
 
 * [PE Architecture Documentation](https://puppet.com/docs/pe/latest/choosing_an_architecture.html)
 * [Classification](documentation/classification.md)
 * [Architectures](documentation/architectures.md)
 * [Testing](documentation/pre_post_checks.md)
 * [Docker Based Examples](documentation/docker_examples.md)
 
-## Requirements
-
-Normally, if you are able to use peadm to set up an infrastructure and Puppet agent runs are all working, chances are you met all the requirements and don't have to worry. Sometimes Some notable requirements are highlighted below which may accidentally be adjusted by users, but which architectures deployed by this module rely on. These configuration requirements need to be maintained for the infrastructure to operate correctly.
-
-* Classifier Data needs to be enabled. This feature is enabled by default on new installs, but can be disabled by users if they remove the relevant configuration from their global hiera.yaml file. See the [PE docs](https://puppet.com/docs/pe/latest/config_console.html#task-5039) for more information.
-
 ## Getting Help
 
-To get help with issues concerning this module, please make use of [issues](https://github.com/puppetlabs/puppetlabs-peadm/issues) in the project on GitHub.
+To get help with issues concerning this module, please make use of [issues](https://github.com/puppetlabs/puppetlabs-peadm/issues) in the project on GitHub.