add definition for standard output logging exporter (#3741)

## Changes

I couldn't find the definition for a standard output exporter for the
logging signal, so I'm submitting one. This is mostly a copy of the
definition already present for the metrics exporter. It doesn't specify
a format for the output itself.

Similar to
#3740

CHANGELOG.md

@@ -18,6 +18,9 @@ release.
 
 ### Logs
 
+- Add definition for standard output log record exporter.
+  ([#3741](https://github.com/open-telemetry/opentelemetry-specification/pull/3741))
+
 ### Resource
 
 ### OpenTelemetry Protocol

specification/logs/sdk_exporters/stdout.md

@@ -0,0 +1,22 @@
+<!--- Hugo front matter used to generate the website version of this page:
+linkTitle: Stdout
+--->
+
+# OpenTelemetry LogRecord Exporter - Standard output
+
+**Status**: [Experimental](../../document-status.md)
+
+"Standard output" LogRecord Exporter is a [LogRecord
+Exporter](../sdk.md#logrecordexporter) which outputs the logs to
+stdout/console.
+
+[OpenTelemetry SDK](../../overview.md#sdk) authors MAY choose the best idiomatic
+name for their language. For example, ConsoleExporter, StdoutExporter,
+StreamExporter, etc.
+
+If a language provides a mechanism to automatically configure a
+[LogRecordProcessor](../sdk.md#logrecordprocessor) to pair with the associated
+exporter (e.g., using the [`OTEL_LOGS_EXPORTER` environment
+variable](../../configuration/sdk-environment-variables.md#exporter-selection)), by
+default the standard output exporter SHOULD be paired with a [simple
+processor](../sdk.md#simple-processor).