update benchmark readme (#72620)
update benchmark readme (#72620)

Documents that version 2.0 of the async profiler doesn't seem to work
with jmh. Fixes some syntax in another profiling example.
GlenRSmith/elasticsearch,robin13/elasticsearch,robin13/elasticsearch,robin13/elasticsearch,robin13/elasticsearch,GlenRSmith/elasticsearch,GlenRSmith/elasticsearch,GlenRSmith/elasticsearch,GlenRSmith/elasticsearch,robin13/elasticsearch