Include CHANGELOG.md in the sdist

[musicinmybrain]

(I suppose you could include Demo.ipynb too, if you wanted.)

$ python3 -m build
$ tar -tzvf dist/pyMapVBVD-0.5.3+1.g17e4c01.tar.gz | grep CHANGE
-rw-r--r-- ben/ben         841 2023-07-07 09:55 pyMapVBVD-0.5.3+1.g17e4c01/CHANGELOG.md