Update readthedocs.yml

# .readthedocs.yml

requirements_file: requirements.txt

version: 2

build:

  image: latest

  os: ubuntu-22.04

  tools:

    python: "3.10"

sphinx:

  builder: html

  configuration: docs/conf.py

formats:

  - pdf

  - epub

python:

  version: 3.6

  install:

   - requirements: requirements.txt