Update Protobuf Java/Kotlin GitHub README.

Removes information on how to build Maven from source since that build path is no longer supported.

Also updates the documentation to cover how to use Kotlin protobufs.

PiperOrigin-RevId: 682382817

java/README.md

@@ -29,7 +29,7 @@ If you are using Maven, use the following:
 
 And **replace `<!--version-->` with a version from the
 [Maven Protocol Buffers Repository](https://mvnrepository.com/artifact/com.google.protobuf/protobuf-java).**
-For example, `3.25.3`.
+For example, `4.28.2`.
 
 Make sure the version number of the runtime matches (or is newer than) the
 version number of the protoc.
@@ -93,49 +93,63 @@ package).
 
 4) Install the classes wherever you prefer.
 
-### Build from Source - With Maven
-
-WARNING: Building from source with Maven is deprecated and will be removed in the 4.28.x release.
+## Kotlin Protocol Buffers
 
-1) Install Apache Maven if you don't have it:
+This directory also provides support for Kotlin protocol buffers, which are
+built on top of Java protocol buffers. Kotlin protocol buffers require a
+dependency on Java protocol buffers, and both Java and Kotlin protocol buffer
+code must be generated for every proto file.
 
-     http://maven.apache.org/
+The main goal of Kotlin protobuf is to provide idiomatic ways to build and read
+protocol buffers in Kotlin. Learn more about Kotlin protobufs in our
+[documentation](https://protobuf.dev/getting-started/kotlintutorial/).
 
-2) Build the C++ code, or obtain a binary distribution of protoc (see
-   the toplevel [README.md](../README.md)). If you install a binary
-   distribution, make sure that it is the same version as this package.
-   If in doubt, run:
-
-     $ protoc --version
+### Use Kotlin Protocol Buffers
 
-   You will need to place the protoc executable in ../src.  (If you
-   built it yourself, it should already be there.)
+To use protobuf in Kotlin, first install the protocol compiler (protoc --
+instructions for installing are in the top-level [README.md](../README.md)) and
+use it to generate Java and Kotlin code for your .proto files:
 
-3) Run the tests:
+```
+$ protoc --java_out=${OUTPUT_DIR} --kotlin_out=${OUTPUT_DIR} path/to/your/proto/file
+```
 
-     $ mvn test
+Include the generated Java and Kotlin files in your project and add a dependency on the
+protobuf Java and Kotlin runtime.
 
-   If some tests fail, this library may not work correctly on your
-   system.  Continue at your own risk.
+### Maven
 
-4) Install the library into your Maven repository:
+If you are using Maven, use the following:
 
-     $ mvn install
+```xml
+<dependency>
+  <groupId>com.google.protobuf</groupId>
+  <artifactId>protobuf-java</artifactId>
+  <version><!--version--></version>
+</dependency>
 
-5) If you do not use Maven to manage your own build, you can build a
-   .jar file to use:
+<dependency>
+  <groupId>com.google.protobuf</groupId>
+  <artifactId>protobuf-kotlin</artifactId>
+  <version><!--version--></version>
+</dependency>
+```
 
-     $ mvn package
+**Replace `<!--version-->` with a version from the
+[Maven Protocol Buffers Repository](https://mvnrepository.com/artifact/com.google.protobuf/protobuf-kotlin),**
+such as `4.28.2`.
 
-   The .jar will be placed in the "target" directory.
+Make sure the version number of the runtimes match each other and match (or are 
+newer than) the version number of the protoc.
 
-The above instructions will install 2 maven artifacts:
+### Use Kotlin Protocol Buffers on Android
 
-  * protobuf-java: The core Java Protocol Buffers library. Most users only
-                   need this artifact.
-  * protobuf-java-util: Utilities to work with protos. It contains JSON support
-                        as well as utilities to work with proto3 well-known
-                        types.
+For Android users, it's recommended to use the Java Lite runtime for its smaller
+code size. We provide a `protobuf-kotlin-lite` package in Maven and Bazel to
+pair with the Java Lite runtime. Use these if you want to use Kotlin on
+Android or in another context where you want to use Java Lite. Similar to the
+full runtime, `protobuf-kotlin-lite` requires a dependency on
+`protobuf-java-lite`.
 
 ## Compatibility Notice
 
@@ -177,8 +191,3 @@ The complete documentation for Protocol Buffers is available via the
 web at:
 
   https://developers.google.com/protocol-buffers/
-
-## Kotlin Protocol Buffers
-
-Code to support more idiomatic Kotlin protocol buffers has been added to the
-repository, and Kotlin support will be launched in the next numbered release.