Note about peoples names and filenames in wallets files

and link to troggle-generated page on svxfiles and logbook trips

handbook/survey/onlinewallet.html

@@ -116,6 +116,10 @@ looks like this:
 Yes, this is <a href="https://en.wikipedia.org/wiki/JSON">a programming format</a>
   (standardised in 2013) and every comma is critical.
 
+<p>When entering people's names it is important not to use any funny characters (such as "?") because
+peoples names here are used by the software to construct filenames for the surveying to-do lists. And "?" (for instance) is illegal
+in filenames on Windows computers.
+
 <h3>"To do" lists for every caver</h3>
 <p>The folder containing all the wallets for the year, e.g.
 <pre>