Update README including C# 8.0

Author: skarllot

README.md

@@ -29,8 +29,9 @@ Not all versions of StyleCop.Analyzers support all features of each C# language
 
 | C# version | StyleCop.Analyzers version | Visual Studio version |
 |------------|----------------------------|-----------------------|
-|  1.0 - 6.0 | v1.0.2 or higher           | VS2015+               |
-|  7.0 - 7.3 | v1.1.0-beta or higher      | VS2017                |
+| 1.0 - 6.0  | v1.0.2 or higher           | VS2015+               |
+| 7.0 - 7.3  | v1.1.0-beta or higher      | VS2017+               |
+|    8.0     | v1.2.0-beta or higher      | VS2019                |
 
 ## Installation