diff --git a/README.md b/README.md
index 99ad57f..54984c5 100644
--- a/README.md
+++ b/README.md
@@ -100,6 +100,9 @@ If you already have a PyPI repo, use `genlocal` first to generate a local db:
 
 `verify` command accepts same arguments as sync, and accepts some new arguments. Please check `./shadowmire.py verify --help` for more information.
 
+> [!TIP]
+> You could set `SHADOWMIRE_IOWORKERS` environment variable to a number to set threads to do local I/O. Defaults to 5.
+
 > [!IMPORTANT]
 > For users switching from Bandersnatch to Shadowmire, you **MUST** run the following commands (with exclusion, of course) before regular syncing:
 >