add some smallish test data

[UnixJunkie]

• a small ligands dataset
• a pair of binding sites
• example commands showing how to use those

[UnixJunkie]

• how to project a molecules in the ph4 points space
• how to compare two molecules/many
• how to compare two BSs/many

[UnixJunkie]

e.g. how to extract ph4 points from a molecule in SDF format; e.g. example usage of the right python script

[UnixJunkie]

put more doc in README.md.
Also put link to published paper.