Improve the getting started instructions in the GC docs

This is still gcroot vs gc.statepoint agnostic.  I'm just trying to clarify the general documentation at this point.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@230393 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed