Merge pull request #469 from humivo/MeterProviderDoc

Add Meter Provider documentation

Author: humivo

src/docs/getting-started/lambda/lambda-python.mdx

@@ -65,6 +65,9 @@ By default, the ADOT Lambda layer uses the [config.yaml](https://github.com/aws-
  which exports telemetry data to AWS X-Ray. To customize the Collector config,
  see the [main Lambda section for custom configuration instructions](/docs/getting-started/lambda#custom-configuration-for-the-adot-collector-on-lambda)
 
+The ADOT Python Lambda Layer can also be configured to set a Meter Provider with an appropriate reader and exporter if the `OTEL_METRICS_EXPORTER` environment variable is set to the values noted [here](https://opentelemetry.io/docs/reference/specification/sdk-environment-variables/#exporter-selection).  
+The `OTEL_EXPORTER_OTLP_PROTOCOL` environment variable should also be set in correlation to the metrics exporter with [these supported values](https://opentelemetry.io/docs/reference/specification/protocol/exporter/#specify-protocol).
+If these environment variables are not set, then a default Meter Provider with no readers will be set and cannot be overriden.
 
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