Merge branch 'coverage-readme' into 'master'

Add coverage badge to README.md

See merge request !320

README.md

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+[![Coverage Status](https://git.astron.nl/lofar2.0/tango/badges/master/coverage.svg)](https://git.astron.nl/lofar2.0/tango/-/jobs/artifacts/master/download?job=unit_test)
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 # Tango Station Control