Add new option to specify behavior if no files found (#104)

* Add new option to specify behavior if no files found

action.yml

@@ -4,10 +4,19 @@ author: 'GitHub'
 inputs: 
   name:
     description: 'Artifact name'
-    required: false
+    default: 'artifact'
   path:
     description: 'A file, directory or wildcard pattern that describes what to upload'
     required: true
+  if-no-files-found:
+    description: >
+      The desired behavior if no files are found using the provided path.
+
+      Available Options:
+        warn: Output a warning but do not fail the action
+        error: Fail the action with an error message
+        ignore: Do not output any warnings or errors, the action does not fail
+    default: 'warn'
 runs:
   using: 'node12'
   main: 'dist/index.js'