JSON formatting + README

[elmurci]

High Level Overview of Change

A couple of minor JSON formatting issues:

• Trailing comma's
• Comma missing between signatures and payload
• Missing value for expTime

And update on README to include the Self-Sovereign Verifiable PayID RFC in the list.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactor (non-breaking change that only restructures code)
• Tests (You added tests for code that already exists, or your new feature included in this PR)
• Documentation Updates
• Release

Before / After

All the examples in the RFC should be valid JSON now.
Self-Sovereign Verifiable PayID should be in the list of RFC's in the README file.

Test Plan

Test that all JSON's validate.
Check that Self-Sovereign Verifiable PayID is in the RFC's list and links to the right document.