Missing documentation in binary_controls.defaults : sync_mode = "tdyn_div_tkh"

[Debraheem]

Following a recent MESA-user mailing list post, I looked into the binary_controls.defaults to find that there no documentation to toggle the 'sync_mode' &control 'tdyn_div_tkh', which exists in $MESA_DIR/binary/private/binary_tides.f90: subroutine sync_spin_to_orbit. The documentation for this control might have been accidentally overlooked?

Should something like the following be added to binary_controls.defaults?

"! + "tdyn_div_tkh" : Each layer is synced independently using tdyn_div_tkh to iteratively calculate the efficiency, given the timescale."

[matthiasfabry]

Good catch!

addressing in #521.