update readme

Author: anthony-nhs

README.md

@@ -223,7 +223,11 @@ You can only use images built from a pull request for testing changes in github
 ## Generating a .trivyignore file
 You can generate a .trivyignore file for known vulnerabilities by either downloading the json scan output generated by the build, or by generating it locally using the scanning images commands above with a make target of scan-image-json
 
-If generated locally, then the output goes into .out/scan_results_docker.json
+If generated locally, then the output goes into .out/scan_results_docker.json.   
+You can use github cli tools to download the scan output file. Replace the run id from the url, and the -n with the filename to download
+```
+gh run download <run id> -n scan_results_docker_fhir_facade_api_arm64.json 
+```
 
 Once you have the scan output, use the following to generate a new .trivyignore file called .trivyignore.new.yaml. Note this will overwrite the output file when run so it should point to a new file and the contents merged with existing .trivyignore file