add requirements.txt , versionize deps

[simonbuehler]

hi,

great writeup and inspiring work, especially the contour refinement approach - i'm trying to adapt it for pokemon TCG detection. but the now curent packages seem to not be compatible ( shapely 1.8 <_>2.0 , opencv 4.3 and mathplotlib ?)
Maybe you have the pinned versions in your workspace or are you interested in an updated requirements.txt if i get it working?