doc: update minimum supported Unity versions (#480)

* remove installation steps for 2019
* update minimum supported Unity versions

Author: sindharta-tanuwijaya

Documentation~/index.md

@@ -11,6 +11,12 @@ It is designed with the following principles in mind:
 
 **Using Timeline 1.4.x or above is recommended.**
 
+## Supported Unity Versions
+
+* Unity `2020.3.45` or higher.
+* Unity `2021.3.19` or higher.
+* Unity `2022.2.8` or higher.
+
 ## Supported Platforms
 
 1. Windows

README.md

@@ -26,22 +26,20 @@ Streaming Image Sequence is designed with the following principles in mind:
 1. Supports multiple OS.
 
 
-Streaming Image Sequence is currently a preview package and the steps to install it 
-differ based on the version of Unity.
+Streaming Image Sequence is currently a preview package and the following steps are required to install it.
 
-* Unity 2019.x  
-  ![PackageManager2019](Documentation~/images/PackageManager2019.png)
-  1. Open [Package Manager](https://docs.unity3d.com/Manual/upm-ui.html) 
-  2. Ensure that **Show preview packages** is checked. 
-  3. Search for *Streaming Image Sequence*.
-  
-* Unity 2020.1  
   ![PackageManager2020](Documentation~/images/PackageManager2020.1.png)
   1. Open [Package Manager](https://docs.unity3d.com/Manual/upm-ui.html) 
   2. Click the **+** button, and choose **Add package from git URL** 
   3. Type in `com.unity.streaming-image-sequence@` followed by the version.  
-     For example: `com.unity.streaming-image-sequence@0.3.2-preview`
-  
+     For example: `com.unity.streaming-image-sequence@0.16.1-preview`
+
+## Supported Unity Versions
+
+* Unity `2020.3.45` or higher.
+* Unity `2021.3.19` or higher.
+* Unity `2022.2.8` or higher.
+
 ## Supported Platforms
 
 1. Windows