DOCS: Fixed typo in index.md (#1952)

FIX: Fixing typo to resolve docf-4184

Co-authored-by: Håkan Sidenvall <hakan.sidenvall@unity3d.com>

Author: Donal-Power

Packages/com.unity.inputsystem/Documentation~/index.md

@@ -11,7 +11,7 @@ Unity supports input through two separate systems, one older, and one newer.
 
 The older system, which is built-in to the editor, is called the [Input Manager](https://docs.unity3d.com/Manual/class-InputManager.html). The Input Manager is part of the core Unity platform and is the default, if you do not install this Input System Package.
 
-This **Input System package** is a newer, more flexible system, which allows you to use any kind of Input Device to control your Unity content. It's intended to be a replacement for Unity's classic Input Manager. It iss referred to as "The Input System Package", or just **"The Input System"**. To use it, you must [install it into your project using the Package Manager](Installation.md).
+This **Input System package** is a newer, more flexible system, which allows you to use any kind of Input Device to control your Unity content. It's intended to be a replacement for Unity's classic Input Manager. It is referred to as "The Input System Package", or just **"The Input System"**. To use it, you must [install it into your project using the Package Manager](Installation.md).
 
 During the installation process for the Input System package, the installer offers to automatically deactivate the older built-in system. ([Read more](Installation.md))