Document recommended flags for GCToolkit

[karianna]

OK, thank you, that makes sense and quite a few of the Garbage Collection tools document the subset of flags that they support. I tried again with the ones you suggested and it worked (although the Maven VM never exited, not sure if that's intentional and whether it "tails" the file?)

Are these "recommended" flags documented somewhere that I missed? Or should they be added? Maybe to the README for the samples to show what do use when one generates the file?

In future it would be great if one could pass the toolkit the flags that were used and it would then be able to handle pretty much any format as long as it's told what the format is.

Originally posted by @massdosage in https://github.com/microsoft/gctoolkit/issues/209#issuecomment-1046738783