Option ´disableDates´ it's not documented

[nicooga]

I see the code from @amittkSharma that enables the option ´disabledDates´ it's merged, but the docs seems to have been overwritten since there's no reference to the option in the README (#76).

Would be good to have this documented.

[hexadecy]

| **disable-dates** | Date[] | Dates to be disabled or not selectable by user.|