docs(Base64ToGallery): update docs

src/plugins/base64togallery.ts

@@ -23,12 +23,13 @@ export class Base64ToGallery {
 
   /**
    * Converts a base64 string to an image file in the device gallery
-   * @param data
-   * @param prefix
+   * @param {string} data The actual base64 string that you want to save
+   * @param {sstring} prefix Prefix the file with a string. Default is 'img_'. Optional.
+   * @returns {Promise} returns a promise that resolves when the image is saved.
    */
   @Cordova()
   static base64ToGallery(data: string , prefix?: string ): Promise<any> {
     return;
   }
 
-}
+}