Document the --passphrase-fd option in the tor manpage

changes/bug19504

@@ -0,0 +1,3 @@
+  o Minor bugfixes (documentation):
+    - Document the --passphrase-fd option in the tor manpage.
+      Fixes bug 19504.

doc/tor.1.txt

@@ -118,6 +118,11 @@ COMMAND-LINE OPTIONS
    directory of your Tor daemon, and make sure that they are owned by the
    user actually running the Tor daemon on your system.
 
+**--passphrase-fd** __FILEDES__::
+    Filedescriptor to read the passphrase from. Ends at the first NUL or
+    newline. Default: read from the terminal.
+
+
 Other options can be specified on the command-line in the format "--option
 value", in the format "option value", or in a configuration file.  For
 instance, you can tell Tor to start listening for SOCKS connections on port