added comment to explain fix

Author: dreamorosi

Diff for: packages/tracing/src/Tracer.ts

@@ -261,6 +261,9 @@ class Tracer implements TracerInterface {
       return this.provider.captureAWSClient(service);
     } catch (error) {
       try {
+        // This is needed because some aws-sdk clients like AWS.DynamoDB.DocumentDB don't comply with the same
+        // instrumentation contract like most base clients. 
+        // For detailed explanation see: https://github.com/awslabs/aws-lambda-powertools-typescript/issues/524#issuecomment-1024493662
         this.provider.captureAWSClient((service as unknown as T & { service: T }).service);
 
         return service;