"First this user must have [a] certificate issued..."

Added 'a' to the sentence "First this user must have certificate issued..." from the subsection "Normal Users"

content/en/docs/reference/access-authn-authz/certificate-signing-requests.md

@@ -199,7 +199,7 @@ To allow signing a CertificateSigningRequest:
 ## Normal user
 
 A few steps are required in order to get a normal user to be able to
-authenticate and invoke an API. First, this user must have certificate issued
+authenticate and invoke an API. First, this user must have a certificate issued
 by the Kubernetes cluster, and then present that certificate to the Kubernetes API.
 
 ### Create private key