README file: added Gradle plugin portal badge and use attribute subst…

…itutions for version and plugin ID

README.adoc

@@ -7,6 +7,10 @@ ifdef::env-github[]
 endif::[]
 
 = Gradle Helm Plugin
+:version: 1.6.1
+:pluginId: org.unbroken-dome.helm
+
+image:https://img.shields.io/gradle-plugin-portal/v/{pluginId}?versionPrefix={version}[link=https://plugins.gradle.org/plugin/{pluginId}/{version}]
 
 This is a suite of Gradle plugins for building, publishing and managing https://www.helm.sh/[Helm] charts.
 
@@ -17,7 +21,7 @@ NOTE: Starting with version 1.0.0, the plugins require Helm 3.+.
 
 * Gradle task types for common Helm CLI commands
 * Build, package and publish Helm charts using a declarative Gradle DSL
-* Resolve placeholders like `${chartVersion}` from chart source files before packaging
+* Resolve placeholders like `$\{chartVersion}` from chart source files before packaging
 * Resolve dependencies between charts using Gradle artifact dependencies
 * Install, upgrade and uninstall releases to/from a Kubernetes cluster
 
@@ -31,13 +35,21 @@ NOTE: Starting with version 1.0.0, the plugins require Helm 3.+.
 
 == Quick Start
 
-Apply the `org.unbroken-dome.helm` plugin to your Gradle project:
+Apply the `{pluginId}` plugin to your Gradle project:
 
 .build.gradle
-[source,groovy]
+[source,groovy,subs="attributes"]
+----
+plugins {
+    id '{pluginId}' version '{version}'
+}
+----
+
+.build.gradle.kts
+[source,kotlin,subs="attributes"]
 ----
 plugins {
-  id 'org.unbroken-dome.helm' version '1.6.1'
+    id("{pluginId}") version "{version}"
 }
 ----