Add README for API

[kthchew]

Issue

Create a README to document the API, #46.

Description

Contains a basic summary of the (two) current endpoints.

It's probably better to use a tool designed for API documentation in the long run (example) but this is a basic start.

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)
• This change requires a documentation update

Test Steps

N/A

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[prayujt]

LGTM!