Fix docker compose command using the slimmed docker image (alshedivat…

…#2351)

Fixing the docker command based on `docker compose [-f <arg>...]
[options] [COMMAND] [ARGS...]` format on the
[website](https://docs.docker.com/compose/reference/#command-options-overview-and-help).
Because the old command would give error: `unknown shorthand flag: 'f'
in -f`

INSTALL.md

@@ -60,7 +60,7 @@ Note that when you run it for the first time, it will download a docker image of
 
 Now, feel free to customize the theme however you like (don't forget to change the name!). Also, your changes should be automatically rendered in real-time (or maybe after a few seconds).
 
-> Beta: You can also use the slimmed docker image with a size below 100MBs and exact same functionality. Just use `docker compose up -f docker-compose-slim.yml`
+> Beta: You can also use the slimmed docker image with a size below 100MBs and exact same functionality. Just use `docker compose -f docker-compose-slim.yml up`
 
 ### Build your own docker image