docs(lambda): Example to guarantee new version creation (#12598)

This is created to provide an example of a workaround for #10136

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Author: flemjame-at-amazon

packages/@aws-cdk/aws-lambda/README.md

@@ -143,6 +143,19 @@ of a new version resource. You can specify options for this version through the
 > of code providers (such as `lambda.Code.fromBucket`) require that you define a
 > `lambda.Version` resource directly since the CDK is unable to determine if
 > their contents had changed.
+>
+> An alternative to defining a `lambda.Version` is to set an environment variable
+> which changes at least as often as your code does. This makes sure the function
+> always has the latest code.
+>
+> ```ts
+> const codeVersion = "stringOrMethodToGetCodeVersion";
+> const fn = new lambda.Function(this, 'MyFunction', {
+>  environment: {
+>    'CodeVersionString': codeVersion
+>  }
+> });
+> ```
 
 The `version.addAlias()` method can be used to define an AWS Lambda alias that
 points to a specific version.