Fix autoconfigure example (#326)

Author: akirayamamoto

autoconfigure/README.md

@@ -21,6 +21,7 @@ Then start the example application with the logging exporter configured:
 ```shell
 java -Dotel.traces.exporter=logging \
      -Dotel.metrics.exporter=logging \
+     -Dotel.logs.exporter=logging \
      -cp build/libs/opentelemetry-examples-autoconfigure-0.1.0-SNAPSHOT-all.jar \
      io.opentelemetry.example.autoconfigure.AutoConfigExample
 ```
@@ -30,6 +31,7 @@ Alternatively, instead of system properties you can use environment variables:
 ```shell
 export OTEL_TRACES_EXPORTER=logging
 export OTEL_METRICS_EXPORTER=logging
+export OTEL_LOGS_EXPORTER=logging
 
 java -cp build/libs/opentelemetry-examples-autoconfigure-0.1.0-SNAPSHOT-all.jar \
      io.opentelemetry.example.autoconfigure.AutoConfigExample
@@ -46,4 +48,4 @@ INFO: 'important work' : ca3938a5793f6f9aba5c757f536a50cb b5e826c981112198 INTER
 ...
 ```
 
-Congratulations! You are now collecting traces using OpenTelemetry.
+Congratulations! You are now collecting traces using OpenTelemetry.