diff --git a/README.md b/README.md
index 94ae01b..def7d83 100644
--- a/README.md
+++ b/README.md
@@ -114,7 +114,7 @@ The `LETSENCRYPT_HOST` variable most likely needs to be the same as the `VIRTUAL
 If you want to create multi-domain ([SAN](https://www.digicert.com/subject-alternative-name.htm)) certificates add the base domain as the first domain of the `LETSENCRYPT_HOST` environment variable.
 
 ##### test certificates
-If you want to create test certificates that don't have the 5 certs/week/domain limits define the `LETSENCRYPT_TEST` environment variable with a value of `true`.
+If you want to create test certificates that don't have the 5 certs/week/domain limits define the `LETSENCRYPT_TEST` environment variable with a value of `true` (in the containers where you request certificates with LETSENCRYPT_HOST). If you want to do this globally for all containers, set ACME_CA_URI as described below.
 
 ##### Automatic certificate renewal
 Every hour (3600 seconds) the certificates are checked and every certificate that will expire in the next [30 days](https://github.com/kuba/simp_le/blob/ecf4290c4f7863bb5427b50cdd78bc3a5df79176/simp_le.py#L72) (90 days / 3) are renewed.