API specification documentation

[AdebayoEmmanuel]

Create a Notion documentation for the API specification following this guideline:

• Name the notion page "PME notification service API specification". #2
• Update the repository's README.md with a link to the notion page.

On the notion page, create sections with the following headings:

• Architecture: image of our solutions architecture and expected flow of data
• APIs and Methods:
• List and describe the API routes that we will be creating for our client to communicate with our API with their accepted options.
• List and describe any API function/methods used in implementing our logic.
• List and describe any 3rd party APIs that we will be using.
• Schema: a JSON representation of what a notification looks like with data types stored as value for property key.

NB: As we build the project further and run tests on the system, add examples to show the technical specification in action, this way we document every new thing we add and test.