Clarify Maven version requirements
The site has been buildable using Maven 3.3.9 for a while now.
# Building Log4j 2
To build Log4j 2, you need a JDK implementation version 1.7 or greater, JDK
-version 9, and Apache Maven.
-Note that building the site requires Maven 3.0.5, while everything else works
-fine with any version of Maven 3.
+version 9, and Apache Maven 3.x.
Log4j 2.x uses the Java 9 compiler in addition to
the Java version installed in the path. This is accomplished by using Maven's toolchains support.
Log4j 2 provides a sample toolchains XML file in the root folder. This may be used by
modifying it and installing the file as toolchains.xml in the .m2 folder or by using
--t ./toolchains-sample.xml when invoking Maven.
+`-t ./toolchains-sample.xml` when invoking Maven.
To perform the license release audit, a.k.a. "RAT check", run.
