Add new runtimes to README (#59)

* Add Python 3.9 to README
* Add .NET 6
* Add dotnet 6 runtime const

Author: datashaman

README.md

@@ -21,6 +21,7 @@ You can write functions in any of the following runtimes and execute them straig
 - Node.js 14
 - Node.js 12
 - Node.js 10
+- Python 3.9
 - Python 3.8
 - Python 3.7
 - Python 3.6
@@ -30,6 +31,7 @@ You can write functions in any of the following runtimes and execute them straig
 - Java 11
 - Java 8
 - Go 1.x
+- .NET 6
 - .NET Core 3.1
 - .NET Core 2.1 
 
@@ -143,4 +145,4 @@ Sidecar does _not_ handle any API Gateway, Databases, Caches, etc. The _only_ th
 
 Sidecar does not provide a way to execute a function via HTTP. You must execute it from your Laravel app through the provided methods.  
 
-If you need those other services, you are encouraged to use the instances that Vapor has set up for you, or set them up yourself. 
+If you need those other services, you are encouraged to use the instances that Vapor has set up for you, or set them up yourself. 

src/Runtime.php

@@ -18,6 +18,7 @@ abstract class Runtime
     public const JAVA_8_LINUX2 = 'java8.al2';
     public const JAVA_8 = 'java8';
     public const GO_1X = 'go1.x';
+    public const DOT_NET_6 = 'dotnet6';
     public const DOT_NET_31 = 'dotnetcore3.1';
     public const DOT_NET_21 = 'dotnetcore2.1';
     public const PROVIDED_AL2 = 'provided.al2';