Update MFA help text documentation link (#4975)

* Update mfa help text with documentation link

* Update en.json

webapp/components/admin_console/mfa_settings.jsx

@@ -86,7 +86,7 @@ export default class MfaSettings extends AdminSettings {
                     helpText={
                         <FormattedHTMLMessage
                             id='admin.service.enforceMfaDesc'
-                            defaultMessage='When true, users on the system will be required to set up [multi-factor authentication]. Any logged in users will be redirected to the multi-factor authentication setup page until they successfully add MFA to their account.<br/><br/>It is recommended you turn on enforcement during non-peak hours, when people are less likely to be using the system. New users will be required to set up multi-factor authentication when they first sign up. After set up, users will not be able to remove multi-factor authentication unless enforcement is disabled.<br/><br/>Please note that multi-factor authentication is only available for accounts with LDAP and email login methods. Mattermost will not enforce multi-factor authentication for other login methods. If there are users on your system using other login methods, it is recommended you set up and enforce multi-factor authentication directly with the SSO or SAML provider.'
+                            defaultMessage="When true, users on the system will be required to set up <a href='https://docs.mattermost.com/deployment/auth.html' target='_blank'>multi-factor authentication</a>. Any logged in users will be redirected to the multi-factor authentication setup page until they successfully add MFA to their account.<br/><br/>It is recommended you turn on enforcement during non-peak hours, when people are less likely to be using the system. New users will be required to set up multi-factor authentication when they first sign up. After set up, users will not be able to remove multi-factor authentication unless enforcement is disabled.<br/><br/>Please note that multi-factor authentication is only available for accounts with LDAP and email login methods. Mattermost will not enforce multi-factor authentication for other login methods. If there are users on your system using other login methods, it is recommended you set up and enforce multi-factor authentication directly with the SSO or SAML provider."
                         />
                     }
                     disabled={!this.state.enableMultifactorAuthentication}