Sampling configuration should discuss DefaultSampler vs. LocalSampler

[SamStephens]

The Sampling documentation describes how to configure sampling rules. However it does not make it clear that by default the DefaultSampler will be used, and for local sampling rules to be preferred to those from the X-Ray control plane, you need to configure the XRayRecorder to use the LocalSampler.

[srprash]

Thanks for bringing the gap to out notice. We will have the doc fixed and updated in our next release.