docs: ensure sortablejs and @types/sortablejs are peers dependencies

BREAKING CHANGE: peer dependencies now required

Author: waynevanson

README.md

@@ -6,14 +6,17 @@ React bindings to [SortableJS](https://github.com/SortableJS/Sortable)
 
 ## Installation
 
+`sortablejs` and `@types/sortbalejs` are peer dependencies. The latter only used if intellisense/typescript is desired.
+
 ```shell
-npm install --save react-sortablejs
+npm install --save react-sortablejs sortablejs
+npm install --save-dev @types/sortablejs
+
 # OR
-yarn add react-sortablejs
+yarn add react-sortablejs sortablejs
+yarn add -D @types/sortablejs
 ```
 
-Please note that `sortablejs` is not required, as it's bundled in this component.
-
 ## Learn
 
 Here is the TLDR of what sortable is: