Add missing translation

locale/en_US/mfa.locale.js

@@ -14,6 +14,7 @@ module.exports = exports = {
     Are you sure you want to continue?
     `,
     disable: 'Disable MFA',
+    enable: 'Enable MFA',
     disable_success: 'MFA was successfully disabled. You\'ll now sign-in normally.',
 
     recover_prompt: 'To recover access to your account, you can enter one of the generated MFA recovery codes:',

locale/en_US/profile.locale.js

@@ -39,4 +39,7 @@ module.exports = exports = {
         many: 'There are NUM_CODES recovery codes remaining.',
     },
     regenerate_recovery: 'Re-generate Recovery Codes',
+
+    mfa_1: 'MFA is a good-practice security measure that requires you to provide a second factor of identification when you sign in from a service or device that makes use of APP_NAME.',
+    mfa_2: 'Once enabled, APP_NAME will prompt you to enter a code when you sign-in with the APP_NAME web interface from a new device. It will also require you to append the code to your password when signing in to a service that uses APP_NAME as a backend.',
 }