fix: documentation on "Well known exporters" and OTEL_TRACES_EXPORTER variable by ecourreges-orange · Pull Request #2023 · open-telemetry/opentelemetry-python

Following the auto-instrumentation README and examples, I encountered 2 inconsistencies between doc and code, so I fixed the documentation:

fix: documentation on "Well known exporters" -> zipkin doesn't exist but zipkin_json and zipkin_proto exist, etc. Thanks @ocelotl
fix: documentation env var is not OTEL_TRACE_EXPORTER but OTEL_TRACES_EXPORTER