Update README.md and package.json

Author: Voltstro

README.md

@@ -23,11 +23,18 @@ Provides extensions to Unity's `NativeArray<T>` that make using .NET's Span<T> w
 #### Prerequisites
 
 ```
-Unity 2021.3.x
+Unity 2020.3.x
+(Unity 2021.3.x is the recommended version however)
 ```
 
 (Newer Unity versions should be fine as well)
 
+#### Unity 2020.3.x Prerequisites
+
+**IF YOU ARE USING UNITY 2020.3.x WITH THIS PACKAGE, READ THIS**. (Newer versions do not need this step!)
+
+`System.Memory` dll is required (this is where `Span<T>` use to come from). This package it self has no direct dependent installation method for `System.Memory`. You can either install it directly into your Unity project from [NuGet](https://www.nuget.org/packages/System.Memory) (by extracting it from the `.nupkg` file), or via an automatic seamless UPM integration, such as [Voltstro UPM](https://github.com/Voltstro/VoltstroUPM#using-unitynuget-packages), [OpenUPM](https://openupm.com/nuget/), or [UnityNuGet](https://github.com/xoofx/UnityNuGet).
+
 ### Installation Methods
 
 There are three main sources on how you can install this package. Pick which ever one suites you the best!

package.json

@@ -3,7 +3,7 @@
   "displayName": "Native Array Span Extensions",
   "version": "1.0.0",
   "description": "Provides extensions to Unity's NativeArray that make using .NET's Span<T> with them easier.",
-  "unity": "2021.3",
+  "unity": "2020.3",
   "keywords": [
     "native",
     "nativearray",