adds v2.x.x migration guide reference in README for findability

CHANGELOG.adoc

@@ -0,0 +1,16 @@
+= Asciidoctor Maven Plugin changelog
+:uri-asciidoctor: http://asciidoctor.org
+:uri-asciidoc: {uri-asciidoctor}/docs/what-is-asciidoc
+:uri-repo: https://github.com/asciidoctor/asciidoctor-maven-plugin
+:icons: font
+:star: icon:star[role=red]
+ifndef::icons[]
+:star: ★
+endif::[]
+
+This document provides a high-level view of the changes introduced on Asciidoctor Maven Plugin by release.
+For a detailed view of what has changed, refer to the {uri-repo}/commits/master[commit history] on GitHub.
+
+== Unreleased
+
+* Add reference to v2-migration-guide in README for better findability

README.adoc

@@ -75,6 +75,12 @@ endif::[]
 
 === Setup
 
+[WARNING]
+====
+2.0.0 version introduced breaking changes.
+If you are upgrading from a previous version, please read the <<v2-migration-guide.adoc#,v2 migration guide>>.
+====
+
 As this is a typical Maven plugin, simply declare the plugin in the `<plugins>` section of your POM file:
 
 [source,xml,subs=attributes+]