DOCATT-8537: Clarified the installation requirements

- Updated the installation instructions to use steps and make it standard compliant
- Also changed the titles to be doc standard compliant (and updated external links pointing there)

Author: unitALG

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

@@ -110,7 +110,7 @@ To prevent conflicts between simulated touchscreen inputs and native mouse and p
 
 The Unity Remote is an app available for iOS and Android which allows using a mobile device for input while running in the Unity Editor. You can find details about the app and how to install it in the [Unity manual](https://docs.unity3d.com/Manual/UnityRemote5.html).
 
-If you would like to try out the Unity Remote app, you can [install](Installation.md#installing-samples) the "Unity Remote" sample that is provided with the Input System package.
+If you would like to try out the Unity Remote app, you can [install](Installation.md#install-samples) the "Unity Remote" sample that is provided with the Input System package.
 
 > [!NOTE]
 > Joysticks/gamepads are not yet supported over the Unity Remote. No joystick/gamepad input from the mobile device will come through in the editor.

Packages/com.unity.inputsystem/Documentation~/Images/InputSystemPackage.png

@@ -8,18 +8,30 @@ uid: input-system-installation
   - [Enabling the new input backends](#enabling-the-new-input-backends)
   - [Installing samples](#installing-samples)
 
-This guide describes how to install and activate the Input System package for your Unity Project.
+This page describes how to install and activate the Input System package for your Unity Project.
 
 > [!NOTE]
-> The new Input System requires Unity 2019.4+ and the .NET 4 runtime. It doesn't work in projects using the old .NET 3.5 runtime.
+> This version of the new Input System requires the .NET 4 runtime. It doesn't work in projects using the old .NET 3.5 runtime. 
+>
+> This package is only compatible with Unity Editor release versions 2021.3 and later. If you are working in a release version of the Editor prior to 2021.3, you need to use the package version that works with that version of the Editor, indicated by the **Release** tag in the [Unity Package Manager](https://docs.unity3d.com/Manual/upm-ui.html) window.
 
-## Installing the package
+## Install the package
 
-To install the new Input System, open Unity's package manager (menu: __Window > Package Manager__). Select the __Input System__ package from the list, then click __Install__.
+To install the new Input System: 
 
-![Install Input System Package](Images/InputSystemPackage.png)
+1. In the main menu of the Unity Editor, go to __Window__ > __Package Manager__ to open the Unity Package Manager. 
 
-## Enabling the new input backends
+2. Select **Unity Registry** from the navigation panel.
+
+3. Select the __Input System__ package from the list.
+
+    The Package Manager automatically selects that version to install by default.
+
+4. Select __Install__, follow any prompts to [enable the backends](#) for the new Input System.
+
+This package also provides several samples that demonstrate how to work with the new Input System, which are also available on the [Unity Package Manager](https://docs.unity3d.com/Manual/upm-ui.html) window. Refer to [Install samples](#install-samples).
+
+## Enable the new input backends
 
 By default, Unity's classic Input Manager (`UnityEngine.Input`) is active, and support for the new Input System is inactive. This allows existing Unity Projects to keep working as they are.
 
@@ -36,7 +48,7 @@ You can find the corresponding setting in __Edit__ > __Project Settings__ > __Pl
 
 When the new input backends are enabled, the `ENABLE_INPUT_SYSTEM=1` C# `#define` is added to builds. Similarly, when the old input backends are enabled, the `ENABLE_LEGACY_INPUT_MANAGER=1` C# `#define` is added. Because both can be enabled at the same time, it is possible for __both__ defines to be 1 at the same time.
 
-## Installing samples
+## Install samples
 
 The Input System package comes with a number of samples. You can install these directly from the Package Manager window in Unity (__Window > Package Manager__). To see the list of samples, select the Input System package in the Package Manager window and click the __Samples__ tab. Then click __Import__ next to any sample name to import it into the current Project.
 

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

@@ -23,7 +23,7 @@ This is because there are a number of different ways to read input using the Inp
 
 ## Which system is enabled?
 
-When installing the new Input System, Unity prompts you to enable the new input system and disable the old one. You can change this setting at any time later, by going to **Edit > Project Settings > Player > Other Settings > Active Input Handling**, [as described here](./Installation.md#enabling-the-new-input-backends).
+When installing the new Input System, Unity prompts you to enable the new input system and disable the old one. You can change this setting at any time later, by going to **Edit > Project Settings > Player > Other Settings > Active Input Handling**, [as described here](./Installation.md#enable-the-input-backends).
 
 There are scripting symbols defined which allow you to use conditional compilation based on which system is enabled, as shown in the example below.
 

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

@@ -236,7 +236,7 @@ The Input System package provides a **Virtual Mouse** component for this purpose
 > [!NOTE]
 > This component is only compatible with the [Unity UI](https://docs.unity3d.com/Manual/com.unity.ugui.html) (uGUI) system, and not UI Toolkit.
 
-To see an example of the Virtual Mouse in a project, see the [Gamepad Mouse Cursor sample](Installation.md#installing-samples) included with the Input System package.
+To see an example of the Virtual Mouse in a project, see the [Gamepad Mouse Cursor sample](Installation.md#install-samples) included with the Input System package.
 
 ### Using the Virtual Mouse component