Update index.md - Citation

docs/src/index.md

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 [![codecov](https://codecov.io/gh/sisl/DividedRectangles.jl/graph/badge.svg?token=YALXFAP7UO)](https://codecov.io/gh/sisl/DividedRectangles.jl)
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+**Important Note**: The content in this package is borrowed from Chapter 7, "Direct Methods," of the forthcoming second edition of "Algorithms for Optimization" by Mykel Kochenderfer and Tim Wheeler.
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 **DividedRectangles.jl** provides an implementation of the DIRECT (DIvided RECTangles) [algorithm for global optimization](https://scholar.google.com/scholar?hl=en&as_sdt=0%2C5&q=Lipschitzian+optimization+without+the+Lipschitz+constant&btnG=). The DIRECT algorithm is particularly useful for optimizing functions where the Lipschitz constant is unknown. This package allows users to perform both univariate and multivariate optimization efficiently.
 
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 Example Objective Function:
 As an example of an objective function, consider: