Add README for Java-based VSS implementation.

java/README.md

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+# Versioned Storage Service (Java)
+
+This directory hosts the Java-based implementation of the Versioned Storage Service (VSS).
+
+### Prerequisites
+
+- Install Gradle (https://gradle.org/install/).
+- Install JDK 17 (https://docs.aws.amazon.com/corretto/latest/corretto-17-ug/).
+- Install Docker (https://docs.docker.com/desktop/).
+- Install PostgreSQL 15 (https://www.postgresql.org/download/).
+
+### Building
+
+```
+git clone https://github.com/lightningdevkit/vss-server.git
+cd vss-server/java
+
+gradle wrapper --gradle-version 8.1.1
+./gradlew build -x test  # Running tests requires docker-engine to be running.
+```
+
+* WAR file for deployment should be generated at `./app/build/libs/vss-1.0.war`
+
+#### Only required for development:
+
+* Generating updated [protobuf] objects:
+    ```
+    ./gradlew generateProto
+    ```
+
+* Generating updated [Jooq] objects:
+    ```
+    ./gradlew generateJooq
+    ```
+
+### Running
+
+#### For local testing with a PostgreSQL container:
+
+```
+    docker-compose up --build
+
+    # To inspect the database:
+    `psql postgresql://postgres:YOU_MUST_CHANGE_THIS_PASSWORD@localhost:5432/postgres`
+```
+
+#### To run just the VSS-server:
+
+1. **Edit Configuration**: Modify the Dockerfile or application.properties to set application configurations and
+   environment variables as needed. Add PostgreSQL endpoint configuration.
+2. Create table in PostgreSQL using `./app/src/main/java/org/vss/impl/postgres/sql/`
+3. **Build the Docker Image**:
+    ```
+        docker build --tag 'vss_server_java'
+    ```
+3. **Run the Docker Container**:
+    ```
+        docker run --detach -p 8080:8080 'vss_server_java'
+    ```
+4. VSS endpoint should be reachable at `http://localhost:8080/vss`.
+
+### Configuration
+
+Refer `./app/src/main/resources/application.properties` to see available configuration options.
+
+Each property can be overridden by setting an environment variable with the same name.
+For example, to override `vss.jdbc.url`, set an environment variable `vss.jdbc.url` with the new value.
+
+### Support
+
+If you encounter any issues or have questions, feel free to open an issue on
+the [GitHub repository](https://github.com/lightningdevkit/vss-server/issues). For further assistance or to discuss the
+development of VSS, you can reach out to us in the [LDK Discord](https://discord.gg/5AcknnMfBw) in the `#vss` channel.
+
+[LDK Discord]: https://discord.gg/5AcknnMfBw
+
+[protobuf]: https://protobuf.dev/
+
+[Jooq]: https://www.jooq.org/