Update README.md

Author: astomodynamics

README.md

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 # Constrained Differential Dynamic Programming (CDDP) solver in C++
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+|   / ___|  _ \|  _ \|  _ \  (_)_ __    / ___| _     _    |
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+|  | |   | | | | | | | |_) | | | '_ \  | |   _| |_ _| |_  |
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+|  | |___| |_| | |_| |  __/  | | | | | | |__|_   _|_   _| |
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+|   \____|____/|____/|_|     |_|_| |_|  \____||_|   |_|   |
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 **This library is actively under construction.** Please wait for proper release after starring this repo :star:
 Also, I am writing this library for practical experience with C++. Any suggestions are helpful to me.