Add templates and many other things

Example Unity Project/Library/PackageCache/com.unity.sysroot@2.0.5/Documentation~/index.md

@@ -0,0 +1,53 @@
+# Unity IL2CPP Build Support for Linux
+
+Support for Linux players using IL2CPP is available from 2019.4 onwards.
+
+Operating systems (OS) have their own build systems which vary from one another. If you build using the headers and libraries on a particular OS, this might result in the built player not running on a different one. To address this, Unity provides a sysroot to build against which works on all supported Linux platforms.
+
+The sysroot also allows cross-compilation support which enables you to build Linux IL2CPP from Linux, macOS and Windows.
+
+## Prerequisites
+
+To use the following packages, you need to install the Linux Build Support (IL2CPP) module in your Unity Editor version. Use the Unity Hub to do this. For further information, see [Adding Modules to the Unity Editor](https://docs.unity3d.com/2021.2/Documentation/Manual/GettingStartedAddingEditorComponents.html).
+
+## Unity toolchain packages
+
+Unity provides a toolchain package, which installs the sysroot and a toolchain, for building binaries for the target. The naming convention for these packages is:
+
+* _host platform and architecture_ 
+* _target platform and architecture_
+
+If the host platform and architecture are the same as the target platform and architecture, shorten the name to platform and architecture.
+
+## Installing a Unity toolchain package
+
+To install a Unity toolchain package:
+1. Go to **Window** > **Package Manager**. 
+2. Use the search bar to find the package, and click **Install** in the bottom right corner of the Package Manager window.  
+3. Choose the package based on the host platform.
+
+| Host    | Package                                  |
+| ------- | ---------------------------------------- |
+| Linux   | com.unity.toolchain.linux-x86_64         |
+| macOS     | com.unity.toolchain.macos-x86_64-linux-x86_64 |
+| Windows | com.unity.toolchain.windows.x86_64-linux-x86_64 |
+
+![Package Manager window](Images/sysroot_PackageManagerScreenshot.png)
+
+## Using a Unity toolchain package:
+
+When you have installed your toolchain package, go to **Project Settings** > **Player** > **Configuration** and set the **ScriptingBackend** to **IL2CPP**.
+
+![Project Settings window](Images/sysroot_ProjectSettingsScreenshot.png)
+
+To build your project:
+1. Go to **File** > **Build Settings**.
+2. In the **Target Platform** dropdown menu, select **Linux**.
+3. Click **Build** or **Build and Run**.
+
+## Technical Details
+
+Requirements:
+
+- Unity version 2019.4.1f1
+- Linux Build Support (IL2CPP) module