Add support for --private to server.js (for my private builds only)

modules/shared/lib/private.js

@@ -38,5 +38,8 @@
  * PRIVATE enables certain private features that we don't want enabled on the public web server, so by default,
  * PRIVATE is false.  For Jekyll configurations, if site.pcjs.private is set, this file gets included, overriding
  * the default.
+ *
+ * Currently, the only (checked-in) use of the private setting is to set the client's PRIVATE global and trigger
+ * the loading of alternate (ie, private) XML files in embed.js.
  */
 PRIVATE = true;