Add testing section to README

[dnogu]

Features

List any features you're adding to this app (e.g. new actions, parameters, auth methods, etc.)

Bug Fixes

Describe any bugs you've fixed in this app, and how they were fixed

Manual Documentation

Have you made any changes that should be documented in manual_readme_content.md?

The following changes require documentation in manual_readme_content.md:

• New, updated, or removed REST handlers
• New, updated, or removed authentication methods, especially complex methods like OAuth
• Compatibility considerations with respect to deployment types (e.g. actions that cannot be run on cloud or an automation broker)

• I have verified that manual documentation has been updated where appropriate

Other information

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