update doc

Author: alexcheng1982

README.md

@@ -2,7 +2,24 @@
 
 [![build](https://github.com/JavaAIDev/easy-llm-tools/actions/workflows/build.yaml/badge.svg)](https://github.com/JavaAIDev/easy-llm-tools/actions/workflows/build.yaml)
 ![Maven Central Version](https://img.shields.io/maven-central/v/com.javaaidev.easyllmtools/llm-tool-spec)
+[![javadoc](https://javadoc.io/badge2/com.javaaidev.easyllmtools/llm-tool-spec/javadoc.svg)](https://javadoc.io/doc/com.javaaidev.easyllmtools/llm-tool-spec)
 
-Build LLM Tools Easily
+**Easy LLM Tools** is a set of tools to create tools used by LLMs, primarily for Java and Spring AI. It consists of three parts:
+
+- LLM tool spec
+- LLM tool code generator
+- LLM tool integrations
+
+Tools play an important role in building AI applications, especially for agents. Agents use tools to access external information and perform actions.
+
+Tools are not hard to create. Different AI frameworks and libraries have their own ways to create tools. These frameworks and tools usually take a **code-first** approach. Tools are directly built using code.
+
+Easy LLM Tools takes a **spec-first** approach. For each tool, its spec should be create first. By creating tool specs, we can enable advanced usage scenarios of tools:
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+- Search of tools using RAG
+- Dynamic invocation of tools
+- Tool UI generation
+- Documentation
+- Share and reuse
 
 See [doc](https://javaaidev.com/docs/easy-llm-tools/intro/)