Add missing commas

Author: fatosmorina

content/tutorial/tutorial.md

@@ -26,7 +26,7 @@ Once you get a little familiar with the game, feel free to close that tab, as we
 
 ### Prerequisites
 
-We'll assume some familiarity with HTML and JavaScript but you should be able to follow along even if you haven't used them before.
+We'll assume some familiarity with HTML and JavaScript, but you should be able to follow along even if you haven't used them before.
 
 If you need a refresher on JavaScript, we recommend reading [this guide](https://developer.mozilla.org/en-US/docs/Web/JavaScript/A_re-introduction_to_JavaScript). Note that we're also using some features from ES6, a recent version of JavaScript. In this tutorial, we're using [arrow functions](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions), [classes](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes), [`let`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/let), and [`const`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/const) statements. You can use <a href="http://babeljs.io/repl/#?babili=false&evaluate=true&lineWrap=false&presets=es2015%2Creact&experimental=false&loose=false&spec=false&code=const%20element%20%3D%20%3Ch1%3EHello%2C%20world!%3C%2Fh1%3E%3B%0Aconst%20container%20%3D%20document.getElementById('root')%3B%0AReactDOM.render(element%2C%20container)%3B%0A">Babel REPL</a> to check what ES6 code compiles to.
 
@@ -494,7 +494,7 @@ Determining how an immutable object has changed is considerably easier. If the o
 
 #### Determining When to Re-render in React
 
-The biggest benefit of immutability in React comes when you build simple _pure components_. Since immutable data can more easily determine if changes have been made it also helps to determine when a component requires being re-rendered.
+The biggest benefit of immutability in React comes when you build simple _pure components_. Since immutable data can more easily determine if changes have been made, it also helps to determine when a component requires being re-rendered.
 
 To learn more about `shouldComponentUpdate()` and how you can build *pure components* take a look at [Optimizing Performance](/docs/optimizing-performance.html#examples).