Update Readme and Configuration Instructions

Problem/Motivation

The current documentation in the readme points to the developer portal without a clear reason to the end user as to what they need to access in the developer portal. Additionally, the readme can be updated to include additional information about the options available for configuration.

Proposed resolution

The link that is in the API credentials section points to the developer portal. However, I don’t believe there is anything in that portal the end user needs. What they need is in the COP / Business Portal https://cop.usps.com/cop-navigator. They need to create and view the details of their app.

I think the readme can be further updated to provide clarity on the options. We should link to this page Getting Started | devportal and indicate that Items 1-3 need to be done by each user of the module. Also, it wouldn’t be bad to have this same note on the configuration form (in order to generate these keys follow steps 1-3 from this setup guide from USPS)

Log In/Create USPS Business Account

Use the USPS Customer Onboarding Portal (COP), sign into your USPS Business Account, or create a new USPS Business Account. The COP will ensure that your USPS Business Account is configured for the USPS APIs.

Create an App

After finishing account setup through the COP, select My Apps on the top of the COP Business Portal page.

Retrieve your Consumer Key and Secret

Within COP, select your App and retrieve your Consumer Key and Consumer Secret from the Credentials section. These credentials are required for generating the OAuth Token.