Fix for spelling mistake and documenting the new behavior of relax_disp.r2eff_read(), when reading r2eff points with the same frequency.
If the spin-container already contain r2eff values with the 'frequency of the CPMG pulse' or 'spin-lock field strength',
the frequency will be changed by a infinitesimal small value of + 0.001 Hz.
This allow for duplicates or more of the same frequency.
