docs: add warning about Maven Wrapper not being supported

README.md

@@ -53,6 +53,16 @@ The Maven template uses some global configuration throughout all jobs.
 | `opts` / `MAVEN_OPTS`               | [Global Maven options](http://maven.apache.org/configure.html#maven_opts-environment-variable)                     | `-Dhttps.protocols=TLSv1.2 -Dmaven.repo.local=${MAVEN_CFG_DIR}/repository -Dorg.slf4j.simpleLogger.showDateTime=true -Djava.awt.headless=true` |
 | `cli-opts` / `MAVEN_CLI_OPTS`       | Additional [Maven options](https://maven.apache.org/ref/3-LATEST/maven-embedder/cli.html) used on the command line | `--no-transfer-progress --batch-mode --errors --fail-at-end --show-version -DinstallAtEnd=true -DdeployAtEnd=true` |
 
+### About `$MAVEN_IMAGE`
+
+Each job in the template will use the defined container image to provide the Maven and Java runtime to the job context.
+That's why it is mandatory that you set the version of Maven as required by your project (e.g. `registry-1.docker.io/library/maven:3.9.9-eclipse-temurin-21` for Maven 3.9.9 on Eclipse Temurin JDK 21).
+
+#### Use of the Maven Wrapper
+
+Maven Wrapper - although very convenient for the developer to automatically download and use the required Maven version on each developer environment - is **not supported by this template**.
+We consider reinstalling over and over again another version of Maven in every job would be dumb: better pull directly an image with the right version.
+			
 ### About `$MAVEN_CFG_DIR`
 
 This variable is used to define the Maven configuration directory. It is used to declare the cache policy and marked the `${MAVEN_CFG_DIR}/repository` directory as cached (not to download Maven dependencies over and over again).