Update doc

doc/nghttpx.h2r

@@ -49,6 +49,9 @@ SIGQUIT
   accepting connection.  After all connections are handled, nghttpx
   exits.
 
+SIGHUP
+  Reload configuration file given in :option:`--conf`.
+
 SIGUSR1
   Reopen log files.
 
@@ -56,7 +59,11 @@ SIGUSR2
   Fork and execute nghttpx.  It will execute the binary in the same
   path with same command-line arguments and environment variables.
   After new process comes up, sending SIGQUIT to the original process
-  to perform hot swapping.
+  to perform hot swapping.  The difference between SIGUSR2 + SIGQUIT
+  and SIGHUP is that former is usually used to execute new binary, and
+  the master process is newly spawned.  On the other hand, the latter
+  just reloads configuration file, and the same master process
+  continues to exist.
 
 .. note::
 

doc/sources/nghttpx-howto.rst

@@ -236,6 +236,9 @@ all existing frontend connections are done, the current process will
 exit.  At this point, only new nghttpx process exists and serves
 incoming requests.
 
+If you want to just reload configuration file without executing new
+binary, send SIGHUP to nghttpx master process.
+
 Re-opening log files
 --------------------