Resolve #3471391 "Update the readme"

Closes #3471391

README.md

+# Project Browser API Browser
+
+The Project Browser API Browser module provides a way to create Project Browsers
+that connect with external APIs to provide the content source. This allows
+organizations to create curated lists of projects for content administrators to
+browse and install.
+
+## Features
+
+The Project Browser API Browser creates a configuration entity named *Service*.
+
+The Service is the endpoint you are connecting to. 
+
+For example, Packagist:
+
+`api_browser.service.packagist.yml`
+
+```
+id: packagist
+name: 'Packagist'
+description: 'Packagist is the main Composer repository. It aggregates public PHP packages installable with Composer.'
+listing:
+  endpoint: 'https://packagist.org/packages/list.json'
+  method: GET
+  auth: no_auth
+  path: packages
+  pagination: true
+  page: ''
+  per_page: ''
+search:
+  -
+    parameter: vendor
+    value: 'drupal'
+  -
+    parameter: type
+    value: 'drupal-recipe'
+  -
+    parameter: 'fields[]'
+    value: 'type'
+  -
+    parameter: 'fields[]'
+    value: 'repository'
+  -
+    parameter: 'fields[]'
+    value: 'abandoned'
+project:
+  enable: true
+  endpoint: 'https://packagist.org/packages/{{item_key}}.json'
+  method: GET
+  auth: no_auth
+  path: package
+field_mapping:
+  type: '{{ type | replace({"drupal-":""}) }}'
+  package_name: '{{ name }}'
+  machine_name: '{{ name }}'
+  url: '{{ repository }}'
+  logo: "{{ url('<front>') }}core/misc/logo/drupal-logo.svg"
+  title: '{{ name | split("/")[1] }}'
+  short_description: '{{ description }}'
+  long_description: '{{ description }}'
+  compatible: '{{ TRUE }}'
+  maintained: '{{ abandoned != TRUE }}'
+  covered: '{{ FALSE }}'
+  active: '{{ abandoned != TRUE }}'
+  star_user_count: '{{ github_stars }}'
+  project_usage_total: '{{ downloads.total }}'
+  created: '{{ (packages | first).time }}'
+  changed: '{{ (packages | last).time }}'
+  author: "{{ (authors| column('name')) | join(', ') }}"
+  categories: ''
+  images: ''
+  warnings: ''
+```
+
+Twig is used for being able to parse and manipulate the data returned from the
+API endpoint to return the needed values for each of the browser requirements.
+
+A derivative is used in the module's code to dynamically generate Project
+Browser Services from these new config entities.
+
+## Post-Installation
+
+Change "Project Browser API Settings" to "API Browser Settings"
+Click Add Service
+
+
+After you install this module, visit the Project Browser API Browser Settings
+page in your Drupal admin. 
+
+In the Admin menu visit:
+Configuration > Development > Project Browser
+Click on API Browser Settings
+
+From there, you can see the services that have already been installed.
+
+After you are content with those, visit the Project Browser's configuration page
+and select the Project Browser Service you want to make available. Save and view
+your changes in the Project Browser.
+
+## Additional Requirements
+
+There is a known issue [#3457003] in Project Browser at the moment and is
+necessary for the required patch.
+
+This module requires Project Browser which is currently in contrib. Once Project
+Browser is merged into core, there should be no changes.
+
+## Recommended modules/libraries
+
+None at this time.
+
+## Similar projects
+
+* [Project Browser Source Example](https://git.drupalcode.org/project/project_browser/-/tree/2.0.x/modules/project_browser_source_example?ref_type=heads)
+  * A Submodule of Project Browser that provides an example browser.
+* [Project Browser Drupal Packagist(https://www.drupal.org/project/pb_drupal_packagist)]
+  * Use packages.drupal.org as the source of information to bring Drupal modules
+    into Project Browser. Helped us understand the power to extending Project
+    Browser!
+* [Project Browser Gitlab](https://www.drupal.org/project/project_browser_gitlab)
+  * Integrates Project Browser with Gitlab in order to browse (and install in
+    the future) projects from a Gitlab instance.