Add ruling authority to Nassau, Duchy of [Risolto]

I've tried to make this list of the dukes of Nassau. It was a bit complicated with the co-rule of F. August and F. William. I think both of them can be used, but only one of them. At least if I've understood the co-rule correct.
Hope it can be a help at least.


Ruling authority of Nassau, duchy of
House of Nassau-Usingen
- (Duke) Frederick August & (Prince) Frederick William, joint rule (1806-1816)
- Frederick August (1806-1816)
House of Nassau-Weilburg
- William (1816-1839)
- Adolph (1839-1866)

Sources:
https://en.wikipedia.org/wiki/Duchy_of_Nassau
https://en.wikipedia.org/wiki/William,_Duke_of_Nassau
https://en.wikipedia.org/wiki/Frederick_William,_Prince_of_Nassau-Weilburg

Added the 4 but Frederick William under the House of Nassau-Weilburg separately.
We can add multiple separate rulers in the ruling authority field, so we can separate them in the database too.