Show proper command in help text of build subcommand

The help text of the build subcommand suggested to use 'compose build' (instead of 'docker-compose build') to rebuild images.

Signed-off-by: Simon Herter <[email protected]>

compose/cli/main.py

@@ -108,7 +108,7 @@ class TopLevelCommand(Command):
 
         Services are built once and then tagged as `project_service`,
         e.g. `composetest_db`. If you change a service's `Dockerfile` or the
-        contents of its build directory, you can run `compose build` to rebuild it.
+        contents of its build directory, you can run `docker-compose build` to rebuild it.
 
         Usage: build [options] [SERVICE...]