Update and rename README.txt to README.md

Author: Selva1910

unity_package/README.md

@@ -0,0 +1,13 @@
+
+# Git Install url: 
+
+```
+https://github.com/juicycleff/flutter-unity-view-widget.git?path=unity_package#master
+```
+Add this URL in the Package Manager to Install the Package Directly to any desired Unity project
+  
+# DOCUMENTATION
+
+Visit https://github.com/juicycleff/flutter-unity-view-widget
+
+unitypackage version: fuw-2022.3.0