SDK tracing: clarify multi-processors scenarios (#338)
SDK tracing: clarify multi-processors scenarios (#338)

* Recommend chaining on processors

Fixes #316

* fix lint

* fix lint2

* example for span chaining

* fix formatting

* Update sdk-tracing.md

* Update sdk-tracing.md

* Update sdk-tracing.md

* remove advanced example, do not encourage implementing helpers in the SDK

* recommend to move implement new common processing scearios out-of-proc

* fix lint

* BatchProcessor -> BatchEporterProcessor

open-telemetry/opentelemetry-specification,open-telemetry/opentelemetry-specification