Add Sea Florida Change to Use Cases in README.md

[PaulRosenthal]

Hello!

Thank you for creating a Leaflet searching capability. I have used it on my website to allow users to search for a location they would like to view sea level information for. I wanted to add it as an additional example use if you think it would be helpful.

Thanks again!

[stefanocudini]

many thanks @PaulRosenthal