RFR: JDK-8041593: Update README-builds.html to refer to jdk9

[Tim Bell]

Hi Erik:

> Here is a minor patch to README-builds.html to update references to 
> jdk8 to jdk9 and fix the part about boot jdk since we now require jdk8.
>
> I realize there is probably a lot more that needs to be fixed in this 
> file, but would like to leave that for another time.
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8041593
> Webrev: http://cr.openjdk.java.net/~erikj/8041593/webrev.root.01

Looks good to me.

Tim