doc & version: added BlackBIRDS reference and updated version (#53)

* Added BlackBird reference and updated version

* Try to fix test failure

* Change back order

* github pytest workflow: setup-python v3 to v4, stop using .python-version file

* removed .python-version file

* gh workflow pytest: removed push triggers to deprected vberenz-ci branch

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Co-authored-by: Vincent Berenz <vincent.berenz@tuebingen.mpg.de>

More descriptive heading

Added reference to paper published in JOSS, updated version number

Updated version name

Merge branch 'master' into dev-vs

Added reference to normflows paper on arXiv and updated version

Fixed acknowledgements in paper and links in readme'

Merge branch 'master' into dev-vs

Version updated

Readme updated