Note in man page where users can file bugs

In addition to inviting users to tell us about bugs, lets say where.

doc/tor.1.txt

@@ -2654,7 +2654,7 @@ SEE ALSO
 BUGS
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-Plenty, probably. Tor is still in development. Please report them.
+Plenty, probably. Tor is still in development. Please report them at https://trac.torproject.org/.
 
 AUTHORS
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