Add TypeScript example

ts/features/steps/composition.ts

@@ -0,0 +1,10 @@
+import { When, Then } from 'cucumber';
+import { expect } from 'chai';
+
+When('the step definitions are written in {word}', function (language: string) {
+  this.language = language
+});
+
+Then("I don't get a warning about undefined steps", function () {
+  expect(this.language).to.equal('TypeScript')
+});