update readme

Author: fumito-ito

README.md

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+# FunctionCalling-FirebaseVertexAI
+
+This library simplifies the integration of the [FunctionCalling](https://github.com/fumito-ito/FunctionCalling) macro into [FirebaseVertexAI](https://github.com/firebase/firebase-ios-sdk/tree/main/FirebaseVertexAI). By using this library, you can directly generate `Tool` objects from Swift native functions, which can then be specified as FunctionCalling when invoking VertexAI.
+
+## Usage
+
+```swift
+
+import FunctionCalling
+import FunctionCalling_FirebaseVertexAI
+import FirebaseVertexAI
+
+// MARK: Declare the container and functions for the tools to be called from FunctionCalling.
+
+@FunctionCalling(service: .llamaOrGemini)
+struct MyFunctionTools {
+    @CallableFunction
+    /// Get the current stock price for a given ticker symbol
+    ///
+    /// - Parameter: The stock ticker symbol, e.g. GOOG for Google Inc.
+    func getStockPrice(ticker: String) async throws -> String {
+        // code to return stock price of passed ticker
+    }
+}
+
+// MARK: You can directly pass the tools generated from objects to the model in VertexAI.
+
+let model = VertexAI.vertexAI().generativeModel(
+    modelName: "gemini-1.5-flash",
+    tools: MyFunctionTools().firebaseVertexAITools
+)
+```
+
+## Installation
+
+### Swift Package Manager
+
+```
+let package = Package(
+    name: "MyPackage",
+    products: [...],
+    targets: [
+        .target(
+            "YouAppModule",
+            dependencies: [
+                .product(name: "FunctionCalling-FirebaseVertexAI", package: "FunctionCalling-FirebaseVertexAI")
+            ]
+        )
+    ],
+    dependencies: [
+        .package(url: "https://github.com/fumito-ito/FunctionCalling-FirebaseVertexAI", from: "0.1.0")
+    ]
+)
+```
+
+## Contributing
+
+Pull requests are welcome. For major changes, please open an issue first to discuss what you would like to change.
+
+Please make sure to update tests as appropriate.
+
+## License
+
+The MIT License