JCF: move the README.md to its standard location for DUNE DAQ repos

[jcfreeman2]

Description

The standard location for a DUNE DAQ package's README.md is in the docs/ subdirectory, rather than the base of the repo; among other things this will allow it to be picked up when documentation is generated by readthedocs- in fact, there is a old, generated README.md which is already picked up - https://dune-daq-sw.readthedocs.io/en/latest/packages/cibmodules/).

This PR gets rid of the old, generated README.md in docs/ and move the recently-written README.md from the base of the repo into docs/.

Type of change

• Documentation (non-breaking change that adds or improves the documentation)
• New feature or enhancement (non-breaking change which adds functionality)
• Optimization (non-breaking change that improves code/performance)
• Bug fix (non-breaking change which fixes an issue)
• Breaking change (whatever its nature)

Testing here is N/A - moving a README.md won't affect unit tests, etc.

Testing checklist

• Unit tests pass (e.g. dbt-build --unittest)
• Minimal system quicktest passes (pytest -s minimal_system_quick_test.py)
• Full set of integration tests pass (dunedaq_integtest_bundle.sh)
• Python tests pass if applicable (e.g. python -m pytest)
• Pre-commit hooks run successfully if applicable (e.g. pre-commit run --all-files)

Comments here on the testing

Further checks

• Code is commented where needed, particularly in hard-to-understand areas
• Code style is correct (dbt-build --lint, and/or see https://dune-daq-sw.readthedocs.io/en/latest/packages/styleguide/)
• If applicable, new tests have been added or an issue has been opened to tackle that in the future.
  (Indicate issue here: # (issue))