Fix typo in README.md

Corrected a typo in the README.md file where an extra square bracket was mistakenly included in the link to the "Async Document Processing Extensions" documentation. This change ensures the link is properly formatted and functional.

README.md

@@ -20,7 +20,7 @@ See the [discussion](https://github.com/langchain4j/langchain4j/discussions/1897
   templates from the classpath,
   but [PromptTemplateSource](langchain4j-kotlin/src/main/kotlin/me/kpavlov/langchain4j/kotlin/prompt/PromptTemplateSource.kt)
   provides extension mechanism.
-- 💾[Async Document Processing Extensions](docs/AsyncIO.md)] support parallel document processing with Kotlin coroutines
+- 💾[Async Document Processing Extensions](docs/AsyncIO.md) support parallel document processing with Kotlin coroutines
   for efficient I/O operations in LangChain4j
 
 ## Installation