[doc] Minimum java version for building is now java10, mention JAVAFX_HOME

BUILDING.md

@@ -1,7 +1,8 @@
 # How to build PMD
 
-PMD uses [Maven](https://maven.apache.org/) and requires [Java 9](http://www.oracle.com/technetwork/java/javase/downloads/index.html)
-for building.
+PMD uses [Maven](https://maven.apache.org/) and requires at least Java 10 for building.
+You can get Java 10 from [Oracle](http://www.oracle.com/technetwork/java/javase/downloads/index.html)
+or from the [OpenJDK Project](http://jdk.java.net).
 
 PMD uses the [maven wrapper](https://github.com/takari/maven-wrapper), so you can simply build PMD as following:
 

docs/pages/pmd/devdocs/building.md

@@ -10,10 +10,9 @@ author: Tom Copeland, Xavier Le Vourch <xlv@users.sourceforge.net>
 
 # Compiling PMD
 
-*   JDK 9 or higher
-*   [Apache Maven](http://maven.apache.org) 3 or later.
+*   JDK 10 or higher
 
-{% include note.html content="While Java 9 is required for building, running PMD only requires Java 7 (or Java 8 for Apex)." %}
+{% include note.html content="While Java 10 is required for building, running PMD only requires Java 7 (or Java 8 for Apex and the Designer)." %}
 
 You’ll need to either check out the source code or download the latest source release. Assuming you’ve got the latest source release, unzip it to a directory:
 

docs/pages/pmd/userdocs/installation.md

@@ -17,6 +17,9 @@ sidebar: pmd_sidebar
     * For Windows: [Winzip](http://winzip.com) or the free [7-zip](http://www.7-zip.org/)
     * For Linux / Unix: [InfoZip](http://www.info-zip.org/pub/infozip/)
 
+{% include note.html content="For executing the Designer (./run.sh designer) using [OpenJDK](http://jdk.java.net) or Java 11, you need additionally [OpenJFX](http://jdk.java.net). Download it, extract it and set the environment variable JAVAFX_HOME." %}
+
+
 ### Installation
 
 PMD is distributed as a zip archive, which includes both [PMD](#running-pmd-via-command-line) and [CPD](/pmd_userdocs_cpd.html).