Add requirement for cython and update docs

[Lennart-Quantware]

What are the issues this pull addresses (issue numbers / links)?

• Documentation of installation was not up date: newest python version 3.11 requires the use of -f flag for specifying the environment.yml file.

• Using the latest anaconda installation (as of 07-08-2023), you will get the following error when importing qiskit_metal after installation:

     old_get_distutils_extension = pyximport.pyximport.get_distutils_extension
                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  AttributeError: module 'pyximport.pyximport' has no attribute 'get_distutils_extension'

  Which is due to the new cython version 3.0.0 which just came out.

Did you add tests to cover your changes (yes/no)?

No, this is not needed since there are no code changes but only an added requirement.

Did you update the documentation accordingly (yes/no)?

yes

Did you read the CONTRIBUTING document (yes/no)?

yes

Summary

Updated documentation of installation according to newest python version 3.11 Added requirement to not use the latest version of cython (3.0.0)

Details and comments

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