Clarified multi-stage builds

Author: jaydrogers

docs/content/docs/3.guide/2.understanding-file-permissions.md

@@ -30,7 +30,7 @@ It's a bummer that we can only set the user and group ID at build time, but it's
 - By default, all our images run `www-data` as the user (`33:33` for Debian and `82:82` for Alpine)
 - We provide a script that can be called at build time to change the UID and GID of `www-data` (called `docker-php-serversideup-set-id`)
 - If you need to update permissions of service files (example: NGINX, Apache, Unit, etc), you can run the `docker-php-serversideup-set-file-permissions` at build
-- We will use a multi-stage build to ensure that the `docker-php-serversideup-set-id` script is not included in the final image
+- We will use a multi-stage build to ensure that the `docker-php-serversideup-set-id` script is not executed in the construction of the final image
 
 ## Example
 Here's an example of ensuring our UID/GID of `www-data` will match the development UID/GID of the host machine, while preserving the default UID/GID of `33:33` for the final image: