[docs] YAML config file for ReadTheDocs added

[jjfumero]

Fix for Read The Docs. Since last week, we are getting the following exception with OpenSSL:

Traceback (most recent call last):
  File "/home/docs/checkouts/readthedocs.org/user_builds/tornadovm/envs/latest/lib/python3.7/site-packages/sphinx/cmd/build.py", line 280, in build_main
    args.pdb)
  File "/home/docs/checkouts/readthedocs.org/user_builds/tornadovm/envs/latest/lib/python3.7/site-packages/sphinx/application.py", line 219, in __init__
    self.setup_extension(extension)
  File "/home/docs/checkouts/readthedocs.org/user_builds/tornadovm/envs/latest/lib/python3.7/site-packages/sphinx/application.py", line 398, in setup_extension
    self.registry.load_extension(self, extname)
  File "/home/docs/checkouts/readthedocs.org/user_builds/tornadovm/envs/latest/lib/python3.7/site-packages/sphinx/registry.py", line 463, in load_extension
    err) from err
sphinx.errors.ExtensionError: Could not import extension sphinx.builders.linkcheck (exception: urllib3 v2.0 only supports OpenSSL 1.1.1+, currently the 'ssl' module is compiled with OpenSSL 1.0.2n  7 Dec 2017. See: https://github.com/urllib3/urllib3/issues/2168)

Problem description: https://github.com/readthedocs/readthedocs.org/issues/10296

Fix: https://github.com/urllib3/urllib3/issues/2168

[jjfumero]

The documentation builder is fixed.