Update docs for 4.0.0 version (nothing major)

Author: Aaron Long

plugin/src/docs/changelog.adoc

@@ -1,4 +1,7 @@
 == Change Log
+* 4.0.0
+** Initial support for Grails 4
+
 * 3.0.5
 ** Add support for getOriginalValue() using config parameter.
 ** Fix #193 StackOverflow with composite ID and Auditable

plugin/src/docs/introduction.adoc

@@ -9,7 +9,8 @@ It also provides a convenient way to add Update and Create user stamping by exte
 [cols="1,2",width="50%",options="header,footer"]
 |====================
 |Grails Version  | Audit Logging Plugin Version
-|3.3.0 and later | 3.0.x
+|4.0.0 and later | 4.0.0
+|3.3.x | 3.0.x
 |3.0.0 to 3.2.0 | 2.0.x
 |2.0.0 to 2.5 | 1.0.x
 |1.3.x | 0.5.5.3
@@ -25,4 +26,4 @@ Please note, that only Hibernate5 is tested during development. If an issue occu
 please file a GitHub issue.
 
 While the plugin can log transactions for a MongoDB DataSource, it currently does not support MongoDB as an audit logging backend.
-If you use this plugin to log MongoDB transactions, you must configure a SQL DataSource for Audit Logging. See Ticket #181.
+If you use this plugin to log MongoDB transactions, you must configure a SQL DataSource for Audit Logging. See Ticket #181.

plugin/src/docs/upgrading.adoc

@@ -1,4 +1,8 @@
-== Upgrading
+== Upgrading to 4.0.x
+
+The 4.0.0 version of the plugin is backwards compatible with 3.0.x. Any existing configuration and customization should work out of the box.
+
+== Upgrading to 3.0.x
 
 The 3.0.x version of the plugin is a major rewrite of the codebase. Therefore you need to upgrade your code for this version.