[dvipdfmx] man example about pdf:trailerid

[Frédéric Moulins]

Hi,

in the dvipdfmx man page, the usage example of the `pdf:trailerid`
command seems to have an extra '0' after the '9' in the second PDF
string.
```
\special{pdf:trailerid [ (0123456789abcdef) (01234567890abcdef) ]}
```
Since both strings are checked to be 16 bytes, trying out the example
doesn't work.

Maybe an example with hex strings would be useful, like:
```
\special{pdf:trailerid [
    <00112233445566778899aabbccddeeff>
    <00112233445566778899aabbccddeeff>
]}
```
as it is convenient for a user to configure the ID strings with an MD5
hash (or any 128-bit hash) of some parameters or content identifying
the file for example.


Best regards,

Frédéric Moulins