Update README for some troubleshooting steps

Author: julianwood

s3-logs-extension-demo-zip-archive/README.md

@@ -35,7 +35,7 @@ cd s3-logs-extension-demo-zip-archive
 1. Run the following command for AWS SAM to deploy the components as specified in the `template.yml` file:
 ```bash
 sam build
-# If you don't have 'Python' or 'make' installed, you can use the option to build using a container which uses a python3.8 Docker container image
+# If you receive build errors or don't have 'Python' or 'make' installed, you can use the option to build using a container which uses a python3.8 Docker container image.  
 # sam build --use-container
 sam deploy --stack-name s3-logs-extension-demo --guided
 ```
@@ -70,4 +70,7 @@ The logging extension also receives the log stream directly from Lambda, and cop
 
 Browse to the [Amazon S3 Console](https://console.aws.amazon.com/S3). Navigate to the S3 bucket created as part of the SAM deployment. 
 
-Downloading the file object containing the copied log stream. The log contains the same platform and function logs, but not the extension logs, as specified during the subscription.
+Downloading the file object containing the copied log stream. The log contains the same platform and function logs, but not the extension logs, as specified during the subscription.
+
+If you receive a `permission denied Extension.LaunchError` in the logs, the extension does not have the neccesary permissions.
+Run `chmod +x logs_api_http_extension.py` and build and deploy the AWS SAM application again.