README.md: Add missing --repo flag in quickstart
In the `--repo` flag was added to the `operator-sdk new`
command, which is required when running with `--dep-manager modules`.
This breaks the Go quickstart since `--repo` isn't mentioned there.
@@ -64,7 +64,7 @@ $ mkdir -p $HOME/projects/example-inc/
# Create a new app-operator project
$ cd $HOME/projects/example-inc/
$ export GO111MODULE=on
-$ operator-sdk new app-operator
+$ operator-sdk new app-operator --repo github.com/example-inc/app-operator
$ cd app-operator
# Add a new API for the custom resource AppService
