improved readme

README.md

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 Welcome to QuantumDNA, a powerful and flexible tool designed to calculate lifetimes, average charge separation, and dipole moments of excited states along DNA. Leveraging the formalism of open quantum systems and based on tight-binding Hamiltonians, QuantumDNA is equipped to handle various tight-binding models. Users can incorporate custom tight-binding parameters from ab initio calculations or experimental data, as well as define their own models, making the tool highly adaptable. QuantumDNA is regularly updated to ensure it remains at the cutting edge and includes a user-friendly interface to be accessible even to researchers less familiar with computer science. Results from several research papers can be reproduced with QuantumDNA.
 
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 ### Key Features