Explain dependencies in README

Author: ktoso

README.md

@@ -14,6 +14,23 @@ Parts of this project are incomplete, not fleshed out, and subject to change wit
 
 The primary purpose of this repository is to create an environment for collaboration and joint exploration of the Swift/Java interoperability story. The project will transition to a more structured approach once key goals have been outlined.
 
+## Dependencies
+
+This project consists of different modules which have different Swift and Java runtime requirements.
+
+**JavaKit** – the Swift macros allowing the invocation of Java libraries from Swift
+
+- **JDK 17+**, any recent JDK installation should be sufficient, as only general reflection and JNI APIs are used by this integration
+- **Swift 6.0+**, because the library uses modern Swift macros
+
+**jextract-swift** – the source generator that ingests .swiftinterface files and makes them available to be called from generated Java sources
+
+- **Swift 6.x development snapshots**, because of dependence on rich swift interface files  
+- **JDK 22+** because of dependence on [JEP-454: Foreign Function & Memory API](https://openjdk.org/jeps/454)
+  - We are validating the implementation using the currently supported non-LTE release, which at present means JDK-23.  
+
+The extract tool may become able to generate legacy compatible sources, which would not require JEP-454 and would instead rely on existing JNI facilities. Currently though, efforts are focused on the forward-looking implementation using modern foreign function and memory APIs. 
+
 ## Development and Testing
 
 This project contains quite a few builds, Swift, Java, and depends on some custom steps.