Improving installation docs.

[sayinserdar]

I have an angular workspace which has one library and one showcase/demo application. While I'm installing the angularfire via ng add @angular/fire it gives me this error Deploy requires an Angular project type of "application" in angular.json.
It was simple enough to solve the problem with specifying project when using this command but it would be really cool if it's mentioned in the docs.

Like,
If you are in a workspace that has multiple projects.Use this command instead

````ng add @angular/fire --project=<ENTER_YOUR_PROJECT_NAME>```