add old filesystem snapshot example invocation

add warning to README that FILEPATH must be set
before use for filesystem snapshots.

AMUN.example

+#!/bin/bash
+
+nice node course.js --prevnext --brand MUN \
+    --logo example.png --link http://example.com/ \
+    http://wikieducator.org/MUN/Outline \
+    /MUN \
+    /MUN \
+        >/tmp/course-AMUN.txt
+

README.md

@@ -46,6 +46,11 @@ This script currently has two very different functions:
 
 Many of the *options* are actually required to produce meaningful output.
 
+To make filesystem snapshots, you **must** set FILEPATH
+at the top of course.js before use.  FILEPATH must be a
+top level directory that exists within your web server
+root (so that the course files can be served to users).
+
 ### Filesystem snapshot
 
     node course.js \