Add fetchJobs option to parallelize submodule updates

README.md

@@ -93,6 +93,11 @@ Refer [here](https://github.com/actions/checkout/blob/v1/README.md) for previous
     # Default: 1
     fetch-depth: ''
 
+    # Number of fetches to perform simultaneously when updating submodules. 0
+    # indicates default (serial updates).
+    # Default: 0
+    fetch-jobs: ''
+
     # Whether to download Git-LFS files
     # Default: false
     lfs: ''