Update README.md

Author: mvsg2

Qiskit/README.md

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 ### Installation
 Pull up a command prompt terminal (any command line interface connected to the internet) and type: `pip install qiskit`
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 #### Linux-based Operating Systems
 If the terminal does not recognize the Python's package installation manager `pip`, then it is recommended to install the latest version of the Python (3.x) first in the system with the root privileges: `sudo apt-get install python3` and then install Qiskit by the above command. 
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+You may also want to setup your `pylatexenc` library to be able to see quantum circuits with `matplotlib` backend: `pip install pylatexenc`