docs: update java sdk documents

Signed-off-by: peefy <[email protected]>

Author: Peefy

README.md

@@ -52,7 +52,50 @@ func main() {
 
 ### Java
 
-See [here](https://github.com/kcl-lang/kcl-java) for more information.
+Refer to [this](https://docs.github.com/en/packages/working-with-a-github-packages-registry/working-with-the-apache-maven-registry#authenticating-to-github-packages) to configure your Maven; set up your GitHub account and Token in the `settings.xml`.
+
+#### Maven
+
+In your project's pom.xml, configure our repository as follows:
+
+```xml
+<repositories>
+    <repository>
+        <id>github</id>
+        <url>https://maven.pkg.github.com/kcl-lang/*</url>
+        <snapshots>
+            <enabled>true</enabled>
+        </snapshots>
+    </repository>
+</repositories>
+```
+
+This way you'll be able to import the above dependency to use the SDK.
+
+```xml
+<dependency>
+    <groupId>com.kcl</groupId>
+    <artifactId>kcl-lib</artifactId>
+    <version>0.8.6</version>
+</dependency>
+```
+
+Write the code
+
+```java
+import com.kcl.api.API;
+import com.kcl.api.Spec.ExecProgram_Args;
+import com.kcl.api.Spec.ExecProgram_Result;
+
+public class ExecProgramTest {
+    public static void main(String[] args) throws Exception {
+        API api = new API();
+        ExecProgram_Result result = api
+                .execProgram(ExecProgram_Args.newBuilder().addKFilenameList("path/to/kcl.k").build());
+        System.out.println(result.getYamlResult());
+    }
+}
+```
 
 ### Python