Update README.md

Signed-off-by: Fabiana 🚀  Campanari <113218619+FabianaCampanari@users.noreply.github.com>

Author: FabianaCampanari

README.md

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-8. **John von Neumann (1932)**  
+8. **John von Neumann (1932)**  <br>
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    * Formalized the mathematics of quantum mechanics and introduced operator theory.
 
    Formula for the density matrix in Hilbert space: