Update README.md

Author: precsim

README.md

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 FEATool Multiphysics™ - _Physics Simulation Made Easy_
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+**IMPORTANT!** Please _DO NOT FORK_ the repository as it creates unnecessary confusion with out of date versions. Only download or install this toolbox from the [official repository](https://www.github.com/precise-simulation).
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 ![FEATool Multiphysics Screenshot](https://raw.githubusercontent.com/precise-simulation/featool-multiphysics/master/featool-multiphysics-screenshot.png)
 
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