Tweak the doc about packaging Gradle plugins (GradleUp#1143)

src/docs/plugins/README.md

@@ -11,10 +11,10 @@ and `relocationPrefix` settings on any `ShadowJar` task.
 A simple Gradle plugin can use this feature by applying the `shadow` plugin and configuring the `shadowJar` task for relocation.
 
 ```groovy
-dependencies {
-  shadow localGroovy()
-  shadow gradleApi()
+apply plugin: 'java-gradle-plugin'
+apply plugin: 'com.gradleup.shadow'
 
+dependencies {
   implementation 'org.jdom:jdom2:2.0.6'
   implementation 'org.ow2.asm:asm:6.0'
   implementation 'org.ow2.asm:asm-commons:6.0'
@@ -25,14 +25,10 @@ dependencies {
 
 tasks.named('shadowJar', com.github.jengelman.gradle.plugins.shadow.tasks.ShadowJar) {
   enableRelocation = true
+  archiveClassifier = ''
 }
 ```
 
-Note that the `localGroovy()` and `gradleApi()` dependencies are added to the `shadow` configuration instead of the
-normal `compile` configuration. These 2 dependencies are provided by Gradle to compile your project but are ultimately
-provided by the Gradle runtime when executing the plugin. Thus, it is **not** advisable to bundle these dependencies
-with your plugin.
-
 ## Publishing shadowed Gradle plugins
 The Gradle Publish Plugin introduced support for plugins packaged with Shadow in version 1.0.0.
 Starting with this version, plugin projects that apply both Shadow and the Gradle Plugin Publish plugin will be