docs(lambda): add note on potential errors when updating lambda functions

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

@@ -11,6 +11,19 @@ const fn = new lambda.Function(this, 'MyFunction', {
 });
 ```
 
+When deployed, this construct creates or updates an existing
+`AWS::Lambda::Function` resource. When updating, AWS CloudFormation calls the
+[UpdateFunctionConfiguration](https://docs.aws.amazon.com/lambda/latest/api/API_UpdateFunctionConfiguration.html)
+and [UpdateFunctionCode](https://docs.aws.amazon.com/lambda/latest/api/API_UpdateFunctionCode.html)
+Lambda APIs under the hood. Because these calls happen sequentially, and
+invocations can happen between these calls, your function may encounter errors
+in the time between the calls. For example, if you update an existing Lambda
+function by removing an environment variable and the code that references that
+environment variable in the same CDK deployment, you may see invocation errors
+related to a missing environment variable. To work around this, you can invoke
+your function against a version or alias by default, rather than the `$LATEST`
+version.
+
 ## Handler Code
 
 The `lambda.Code` class includes static convenience methods for various types of