Add NCalc documentation with examples for expression evaluation

Author: vivekkpatel

docs/Packages/NCalc.md

@@ -0,0 +1,25 @@
+## Overview
+- NCalc is a fast and lightweight expression evaluator library for .NET
+- designed for flexibility and high performance.
+- It supports a wide range of mathematical and logical operations.
+- Use `dotnet add package NCalcSync` to install nuget package
+- Add `using NCalc;` 
+
+## Simple Expression
+
+```csharp
+var expression = new Expression("2 + 3 * 5");
+Console.WriteLine($"Result: {expression.Evaluate()}");
+```
+## Equations with variables
+```csharp
+string exprText = "2 + 3 * x - Sin(y)";
+
+var expr = new Expression(exprText);
+
+expr.Parameters["x"] = 4;
+expr.Parameters["y"] = Math.PI / 2;
+
+var result = expr.Evaluate();    // result = 2 + 3*4 - 1 = 13
+Console.WriteLine(result);
+```