Fix jre setup documentation

[josephtaylor]

...
    <p>
        Download the following files from the <a
            href="http://www.oracle.com/technetwork/java/javase/downloads/index.html">Oracle website</a>:
    </p>

    <ul>
        <li>Windows x64 Server JRE 8u31</li>
        <li>Linux x64 Server JRE 8u31</li>
        <li>Mac OSX x64 JRE 8u31</li>
    </ul>

    <p>and place them in your local maven repository as</p>

    <ul>
        <li>~/.m2/repository/com/oracle/server-jre/8.31/server-jre-8.31-windows-x64.tar.gz</li>
        <li>~/.m2/repository/com/oracle/server-jre/8.31/server-jre-8.31-linux-x64.tar.gz</li>
        <li>~/.m2/repository/com/oracle/jre/8.31/jre-8.31-macosx-x64.tar.gz</li>
    </ul>
...

When I first read this, I just tried to copy the files into those specific locations. That doesn't work of course, they have to be installed via the maven install command. Seems like the documentation could benefit from that detail.

Here's the commands I used, assuming the tar.gz files are in the current dir

mvn install:install-file -DgroupId=com.oracle \
-DartifactId=server-jre \
-Dclassifier=windows-x64 \
-Dtype=tar.gz \
-Dversion=8.74 \
-Dpackaging=tar.gz \
-Dfile=server-jre-8u74-windows-x64.tar.gz

mvn install:install-file -DgroupId=com.oracle \
-DartifactId=server-jre \
-Dclassifier=linux-x64 \
-Dtype=tar.gz \
-Dversion=8.74 \
-Dpackaging=tar.gz \
-Dfile=server-jre-8u74-linux-x64.tar.gz

mvn install:install-file -DgroupId=com.oracle \
-DartifactId=jre \
-Dclassifier=macosx-x64 \
-Dtype=tar.gz \
-Dversion=8.74 \
-Dpackaging=tar.gz \
-Dfile=jre-8u74-macosx-x64.tar.gz

Not sure if this is something that people are expected to know, but just wanted to note that it threw me off for a little bit.