diff --git a/README.md b/README.md
index f3777fb..5d01550 100644
--- a/README.md
+++ b/README.md
@@ -11,6 +11,9 @@ This is intended for use with Google Sheets via:
 =CURRENTCPI("{bls-token}")
 ```
 
+where `{bls-token}` is the value issued after registering with
+[bls.gov](https://www.bls.gov/developers/home.htm).
+
 ## deployment
 
 Just like [this