update readme with better gradle instruction (#10740)

modules/openapi-generator/src/main/resources/Java/libraries/okhttp-gson/README.mustache

@@ -19,7 +19,7 @@
 
 Building the API client library requires:
 1. Java {{#java8}}1.8{{/java8}}{{^java8}}1.7{{/java8}}+
-2. Maven/Gradle
+2. Maven (3.8.3+)/Gradle (7.2+)
 
 ## Installation
 
@@ -55,7 +55,14 @@ Add this dependency to your project's POM:
 Add this dependency to your project's build file:
 
 ```groovy
-compile "{{{groupId}}}:{{{artifactId}}}:{{{artifactVersion}}}"
+  repositories {
+    mavenCentral()     // Needed if the '{{{artifactId}}}' jar has been published to maven central.
+    mavenLocal()       // Needed if the '{{{artifactId}}}' jar has been published to the local maven repo.
+  }
+
+  dependencies {
+     implementation "{{{groupId}}}:{{{artifactId}}}:{{{artifactVersion}}}"
+  }
 ```
 
 ### Others