chore: traces documentation

Author: surbhigarg92

README.md

@@ -421,6 +421,32 @@ SpannerOptions options = SpannerOptions.newBuilder()
 
 Spanner spanner = options.getService();
 ```
+#### OpenTelemetry SQL Statement Tracing
+The OpenTelemetry traces that are generated by the Java client include any request and transaction
+tags that have been set. The traces can also include the SQL statements that are executed. Enable
+this with the `enableExtendedTracing` option:
+
+```
+SpannerOptions options = SpannerOptions.newBuilder()
+  .setOpenTelemetry(openTelemetry)
+  .setEnableExtendedTracing(true)
+  .build();
+```
+
+This option can also be enabled by setting the environment variable
+`SPANNER_ENABLE_EXTENDED_TRACING=true`.
+
+#### OpenTelemetry API Tracing
+You can enable tracing of each API call that the Spanner client executes with the `enableApiTracing`
+option. These traces also include any retry attempts for an API call:
+  
+```
+SpannerOptions options = SpannerOptions.newBuilder()
+.setOpenTelemetry(openTelemetry)
+.setEnableApiTracing(true)
+.build();
+```
+  
 
 ## Migrate from OpenCensus to OpenTelemetry