Add types for TS

Author: Josh Sirota

types/index.d.ts

@@ -0,0 +1,17 @@
+// Declaration file for Javascript and Node OpenFeature Split Provider
+// Project: http://www.split.io/
+
+import { Provider } from "@openfeature/js-sdk";
+
+export = SplitProvider;
+
+declare module SplitProvider {
+  export interface SplitProviderOptions {
+    splitClient: SplitIO.IClient;
+  }  
+
+  /**
+   * OpenFeature Split Provider constructor.
+   */
+  export function OpenFeatureSplitProvider(options: SplitProviderOptions): Provider;
+}