DWaveSampler docs for the returned SampleSet

Currently the `SampleSet` returned by the `DWaveSampler` contains information in the info field. E.g.
```
>>> DWaveSampler().sample_ising({0: 0}, {}).info
{'timing': {'total_real_time': 7757,
'qpu_access_overhead_time': 824,
'anneal_time_per_run': 20,
'post_processing_overhead_time': 315,
'qpu_sampling_time': 164,
'readout_time_per_run': 123,
'qpu_delay_time_per_sample': 21,
'qpu_anneal_time_per_sample': 20,
'total_post_processing_time': 315,
'qpu_programming_time': 7593,
'run_time_chip': 164,
'qpu_access_time': 7757,
'qpu_readout_time_per_sample': 123}}
```
the docs for the `DWaveSampler` should explain where to find this list. Right now it only contains timing so perhaps should link to [timing-related fields](https://docs.dwavesys.com/docs/latest/c_timing_5.html?highlight=qpu_access_time#timing-related-fields)?