fix README about CRL in usage section

README.md

@@ -50,7 +50,8 @@ From here, you are able to procude certificates from `cfssl` command line with s
 In this example :
 * self signed root ca is installed.
 * this root ca is served via [HTTP API server](https://github.com/cloudflare/cfssl/tree/master/doc/api) for X509 certificates.
-* a CRL is generated is `$cfssl::crldir` directory, updated periodicaly.
+* a CRL is generated in `$cfssl::crldir` directory, updated periodicaly as defined by `$cfssl::crl_gentimer`.
+* the CRL have a duration of validity defined by `cfssl::crl_expiry`
 
 ```
 class { 'cfssl':
@@ -74,7 +75,8 @@ In this example :
 * a self signed root authority is installed.
 * an intermediate authority signed by root authority is installed.
 * this intermediate authority is served via [HTTP API server](https://github.com/cloudflare/cfssl/tree/master/doc/api) for X509 certificates.
-* a CRL is generated is `$cfssl::crldir` directory, updated periodicaly.
+* CRL are generated in `$cfssl::crldir` directory, updated periodicaly as defined by `$cfssl::crl_gentimer`.
+* the CRL have a duration of validity defined by `cfssl::crl_expiry`
 
 ```
 class { 'cfssl':