Correct documentation.

README.md

@@ -258,11 +258,11 @@ You will need to wipe content of `/etc/letsencrypt` volume before container re-c
 
 ### Auto-export certificates in PFX format
 
-Some services need the SSL key and certificate stored together in PFX format (also known as PKCS#12) whose extension is .pfx (or .p12). For this purpose one can set the container environment variable `EXPORT_PFX (default: false)` to `true`: in this case, the container will ensure that every certificate handled by Certbot is exported in PFX format during certificate creation, renewal or container start/restart.
+Some services need the SSL key and certificate stored together in PFX format (also known as PKCS#12) whose extension is .pfx (or .p12). For this purpose one can set the container environment variable `PFX_EXPORT (default: false)` to `true`: in this case, the container will ensure that every certificate handled by Certbot is exported in PFX format during certificate creation, renewal or container start/restart.
 
 The PFX certificate for a given primary domain is located in the container on `/etc/letsencrypt/[DOMAIN]/cert.pks`: it contains the key, certificate and all intermediate certificates.
 
-By default, the PFX certificates are not protected by a passphrase. You can define one using the environment variable `EXPORT_PFX_PASSPHRASE`.
+By default, the PFX certificates are not protected by a passphrase. You can define one using the environment variable `PFX_EXPORT_PASSPHRASE`.
 
 ### Sleep time