Add usage to script

scripts/cactl

@@ -69,3 +69,20 @@ revoke_cert() {
 view_crl() {
   openssl crl -in crl/intermediate.crl.pem -noout -text
 }
+
+operation=$1
+case $operation in
+  cert)     create_cert "$@" ;;
+  crl)      view_crl ;;
+  revoke)   revoke_cert "$@" ;;
+  init)     create_ca "$@" ;;
+
+  '')
+    printf 'usage: cactl <operation>\n'
+    printf 'operations:\n'
+    printf '  cactl cert <domain>   Create a new certificate\n'
+    printf '  cactl crl             View revoked certificates\n'
+    printf '  cactl revoke <domain> Revoke a certificate\n'
+    printf '  cactl init            Initialise a new CA\n'
+  ;;
+esac