Added a small comment on logfile rotation.

doc/latex/httpd.tex

@@ -176,8 +176,10 @@ one argument, a \ex{httpd\=options}-record:
   \sharpf\ means infinite. \semvar{logfile} is either a string, then
   it is the file name of the logfile, or a port, where the log entries
   are written to, or \sharpf, that means no logging is made. The
-  logfile is in Common Log Format (CLF). \semvar{syslog?} tells the
-  server to write syslog messages (\sharpt) or not (\sharpf).
+  logfile is in Common Log Format (CLF). To allow rotation of
+  logfiles, the server will reopen the logfile when it receives the
+  signal \texttt{USR1}. \semvar{syslog?}  tells the server to write
+  syslog messages (\sharpt) or not (\sharpf).
 \end{desc}   
 
 \subsubsection*{Path handlers}