Provide actionable instructions on a format failure in pull requests (#190)

When format failures occur they point out the files and line numbers, but not the command that will automatically fix the problems. As part of the GitHub workflow job this patch will echo the command that you can run with swiftly to auto-fix the formatting problems.

Author: cmcgee1024

.github/workflows/pull_request.yml

@@ -55,5 +55,5 @@ jobs:
       linux_os_versions: "[\"jammy\"]"
       linux_exclude_swift_versions: "[{\"swift_version\": \"nightly-main\"},{\"swift_version\": \"nightly-6.0\"},{\"swift_version\": \"5.8\"},{\"swift_version\": \"5.9\"},{\"swift_version\": \"5.10\"}]"
       linux_pre_build_command: ./scripts/prep-gh-action.sh
-      linux_build_command: swift run swiftformat --lint --dryrun .
+      linux_build_command: swift run swiftformat --lint --dryrun . || (echo "Please run 'swift run swiftformat .' to format the source code."; exit 1)
       enable_windows_checks: false