tor-gencert.1: fix --passphrase-fd description

changes/bug19505

@@ -0,0 +1,5 @@
+  o Minor bugfixes (documentation):
+    - Fix the description of the --passphrase-fd option in the tor-gencert
+      manpage.  The option is used to pass the number of a file descriptor to
+      read the passphrase from, not to read the file descriptor from.  Fixes
+      bug 19505.

doc/tor-gencert.1.txt

@@ -68,7 +68,7 @@ OPTIONS
     Number of months that the certificate should be valid. Default: 12.
 
 **--passphrase-fd** __FILEDES__::
-    Filedescriptor to read the file descriptor from. Ends at the first NUL or
+    Filedescriptor to read the passphrase from. Ends at the first NUL or
     newline. Default: read from the terminal.
 
 **-a** __address__:__port__::