Add README.md

README.md

+Wanna take a look at the colors in our historic postcards?
+Thanks to Laura Wrubel from the George Washington University Libraries in Washington DC, now you can!
+
+We took [her code](https://nbviewer.jupyter.org/github/LibraryOfCongress/data-exploration/blob/master/Dominant%20colors.ipynb),
+adapted it to use [our postcards](https://labs.onb.ac.at/en/dataset/akon/) as a data source,
+tweaked the computation algorithm a little,
+and the results can be seen on [https://labs.onb.ac.at/en/topic/akon-swatches/](https://labs.onb.ac.at/en/topic/akon-swatches/).
+
+Here, you find the two Jupyter Notebooks we used to tweak the algorithm,
+a Python script to actually compute the color data (this takes us about 4 hours),
+and a `requirements.txt` for your own Python virtual environment.
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