Add now auto-generated manpage to svn:ignore

I had to touch svn directly, where is my reimbursement?

Corresponding to flashrom svn r1729.

Signed-off-by: Stefan Tauner <stefan.tauner@alumni.tuwien.ac.at>
Acked-by: Stefan Tauner <stefan.tauner@alumni.tuwien.ac.at>