Add E4ST (#1563)

Author: AbdulSalam416

README.md

@@ -540,7 +540,7 @@ Your contribution is essential to [keep this initative alive](https://opencollec
 - [CairnOpen](https://github.com/CEA-Liten/CairnOpen) - Simulation and optimization software for energy and environmental systems.
 - [osier](https://github.com/arfc/osier) - Justice oriented energy system optimization framework.
 - [STEPS](https://gitee.com/lichgang/steps/) - An open source power system simulator designed for balanced large-scale AC-DC hybrid power system analysis.
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+- [E4ST](https://github.com/e4st-dev/E4ST.jl) - A modeling and optimization framework for integrated energy systems.
 
 ### Energy Markets