#10 Add note about using Java8 to developer guide

docs/developing.asciidoc

@@ -14,18 +14,27 @@ include::_attributes.asciidoc[]
 
 include::dev-env-setup.asciidoc[]
 
+[[maven-build]]
 == Building with Maven
 
+[CAUTION]
+====
+{trace} should be built using a _Java 1.8 VM_.
+The JDK can be downloaded from e.g. https://www.oracle.com/technetwork/pt/java/javase/downloads/jdk8-downloads-2133151.html[Oracle] or https://adoptium.net/archive.html?variant=openjdk8&jvmVariant=hotspot[Adoptium]. +
+To test which Java version is used by Maven, type `mvn -version` in a command shell.
+====
+
 To build {trace} with Maven execute the following command in the root:
 
 Linux :: `./build.sh`
 Windows :: `.\build.cmd`
+Other :: `mvn -Dtycho.pomless.aggregator.names=releng,temporallogic,trace,jfreechart`
 
 NOTE: In the remainder of this document this command will be referred to as `build.sh`
 
 == License header
 
-The Maven build uses https://github.com/mycila/license-maven-plugin[license-maven-plugin] to determine if the link:../releng/legal-defaults/license-header.txt[correct license headers] are used for source files.
+The <<maven-build, Maven build>> uses https://github.com/mycila/license-maven-plugin[license-maven-plugin] to determine if the link:../releng/legal-defaults/license-header.txt[correct license headers] are used for source files.
 If the header is incorrect the build fails.
 
 Handy commands: