Use main instead of master in the readme

Author: hross

README.md

@@ -15,7 +15,7 @@ If you are new, there's also a simpler introduction.  See the [Hello World JavaS
 
 Click the `Use this Template` and provide the new repo details for your action
 
-## Code in Master
+## Code in Main
 
 Install the dependencies  
 ```bash