Fix credentials_file flag in README
diff --git a/README.md b/README.md
index 619efd8..f8e4995 100644
@@ -114,8 +114,9 @@
Your http server's address in the format of host:port
- -username_password string
- (eg 'username:password') credentials for your server. Leave blank to bypass authentication.
+ -credentials_file string
+ File containing credentials for your server. Leave blank to bypass authentication.
+ File should have exactly one line of the form 'username:password'.
Absolute path to your server's Certificate Authority root cert. Downloading all roots currently recommended by the Google Internet Authority is a suitable alternative https://pki.google.com/roots.pem. Leave blank to connect using http rather than https.