fix grammatical error

Author: amirkx

README.md

@@ -10,7 +10,7 @@ marketplace](https://img.shields.io/badge/marketplace-create--env--file-blue?log
 
 ## About
 
-A Github Action to create a '.env' file with Github Secrets. This is useful when
+A Github Action to create an '.env' file with Github Secrets. This is useful when
 you are creating artifacts that need to contain secrets stored in Github
 Secrets. This creates a file with variables that are defined in the Action
 config.