Add tested matrix to readme

[gfardell]

We will add to the readme notes on the tested versions of the CIL plugins and dependancies.

After which we will removed the run_constrained constraint from the conda meta.yaml.

[gfardell]

https://github.com/TomographicImaging/CIL/blob/master/scripts/requirements-test.yml

[casperdcl]

huge amount of sources & (out of sync) duplication already:

• https://github.com/TomographicImaging/CIL/blob/master/scripts/requirements-test.yml
• https://github.com/TomographicImaging/CIL/blob/master/scripts/create_local_env_for_cil_development.sh
• https://github.com/TomographicImaging/CIL/blob/master/recipe/conda_build_config.yaml
• https://github.com/TomographicImaging/CIL/blob/master/recipe/meta.yaml
• https://github.com/TomographicImaging/CIL/blob/master/.github/workflows/build.yml
• https://github.com/TomographicImaging/Build-scripts/tree/main/env_files
• https://github.com/SyneRBI/SIRF-SuperBuild/blob/master/docker/requirements.yml