OpenJ9 support / more exact wording

[bmarwell]

Hi everyone!

Thanks for sharing such a great tool! I would love to try it, but it seems that it is only compatible with HotSpot JVMs.
Consider this sentence from your README:

GCToolKit is a set of libraries for analyzing Java garbage collection (GC) log files

It should probably be:

GCToolKit is a set of libraries for analyzing Hotspot Java garbage collection (GC) log files

I know MS' JVM is yet another hotspot distribution like 99% of the other JVMs out there, but OpenJ9 does have a significant use case and is typically used in conjunction with OpenLiberty.

Many thanks,
- Ben

[karianna]

Now #21 - Pull requests welcome!