Move FastAPI example from README.md to a separate directory

[Ali Aliyev]

Description

The current project structure needs to be slightly tweaked.

This issue concerns only putting the FastAPI example into a separate mini-package. In this case users can run the example and try the library in action.

• Move the FastAPI example into a separated directory from the README.md.
  • Think over what kind of temporary data storage can be used. The data storage can only store data in memory.
  • Create examples/fastapi directory.
  • Create examples/fastapi/README.md with description how run FastAPI project.
  • Create examples/fastapi/requirements.txt with all required requirements.