Update README.md

Author: codeadamca

README.md

@@ -1,3 +1,5 @@
 # php-dropbox-api
 
 A basic example of uploading a file to your Dropbox account using vanilla PHP and a generated access token.
+
+This cose sample uses a ```.env``` files as described on the [php-env](https://github.com/codeadamca/php-env) repo.