Update README.md: Rephrase section about file location to make defaul…

…t locations clear

README.md

@@ -13,7 +13,9 @@ This plugin is distributed under the [GNU GPL v3 license](https://github.com/ope
 
 ### pg_service.conf location
 
-Before using the plugin, make sure you've set the `PGSERVICEFILE` environment variable pointing to the `pg_service.conf` file path.
+If your `pg_service.conf` file is located at `/home/YOUR_USER/.pg_service.conf` (on Linux) or at `%APPDATA%\postgresql\.pg_service.conf` (on Windows), then you are done! The plugin will read your file directly.
+
+If that's not the case, i.e., if your `pg_service.conf` file is not in the aforementioned locations, you can still set the `PGSERVICEFILE` environment variable pointing to your `pg_service.conf` file path before using the plugin.