RADME: about JavaStdlib targets

Author: ktoso

Sources/JavaStdlib/README_PACKAGE_CONVENTION.md

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+# Extracted Java Modules
+
+This directory contains Swift bindings for common Java standard library packages. 
+These pre-built bindings to solve a circular dependency problem - SwiftJava tools need these types to process and generate other bindings.
+
+You can also use these bindings directly in your SwiftJava programs to call Java classes without having to generate wrappers each time.
+
+The naming follows this pattern: Java package names become Swift target names. Example: `java.lang.util` becomes `JavaLangUtil`.
+
+Since Swift doesn't have namespaces like Java, all types appear at the top level in Swift. To avoid naming conflicts, 
+some types may be prefixed with 'J' (e.g. `JList` to avoid confusion with Swift native types).
+
+To see which Java types are included and any naming changes, check the `swift-java.config` file in each module.