[8.x] add details about environment-specific .env files (#7464)

* add details about APP_ENV-specific .env files

* Update configuration.md

Co-authored-by: Taylor Otwell <[email protected]>

Author: Celant

configuration.md

@@ -35,6 +35,11 @@ If you are developing with a team, you may wish to continue including a `.env.ex
 
 Your `.env` file should not be committed to your application's source control, since each developer / server using your application could require a different environment configuration. Furthermore, this would be a security risk in the event an intruder gains access to your source control repository, since any sensitive credentials would get exposed.
 
+<a name="additional-environment-files"></a>
+#### Additional Environment Files
+
+Before loading your application's environment variables, Laravel determines if either the `APP_ENV` environment variable has been externally provided or if the `--env` CLI argument has been specified. If so, Laravel will attempt to load an `.env.[APP_ENV]` file if it exists. If it does not exist, the default `.env` file will be loaded.
+
 <a name="environment-variable-types"></a>
 ### Environment Variable Types