Merge pull request #10740 from bparees/pem

document imageimport pem file argument

install_config/master_node_configuration.adoc

@@ -671,6 +671,12 @@ permission to create Images or ImageStreamMappings via the API are not affected
 this policy - typically only administrators or system integrations will have those
 permissions.
 
+|`*AdditionalTrustedCA*`
+|Specified a filepath to a PEM-encoded file listing additional certificate authorities
+that should be trusted during imagestream import.  This file needs to be accessible
+to the API server process.  Depending how your cluster is installed, this may require
+mounting the file into the API server pod.
+
 |`*InternalRegistryHostname*`
 |Sets the hostname for the default internal image
 registry. The value must be in `*hostname[:port]*` format.