suggest of reference addition

[nbehrnd]

The objective of the PR here only is to use the same vocabulary in the documentation as used by the underlying source code. While preparing the PR, your talk We need to talk about Kekulization, Aromaticity and SMILES delivered at the 254th ACS National Meeting in Washington, DC Aug 2017 was found.

This reference, and possibly Karl Theis' answer here likely provide a nice initial context for those dealing for the first time with Kekulization failures, the third criterion partialsmiles checks, as an addition.