dx component add fails to add component

Hi there,

I've started a new project (`dx new`) with `workspace`.

I get this error when trying to add the `button` component.

```console
$ dx components add button

ERROR dx components: Failed to find binary package to build.
You need to either run dx from inside a binary crate or specify a binary package to build with the `--package` flag. Try building again with one of the binary packages in the workspace:
- desktop
- mobile
- web
```

I've tried adding `--module-path packages/ui` with no success

Edit:

If I `cd packages/ui/` it does work, but it leaves me confused with the output:

```
Created new components module at /home/woile/projects/reciperium/sweetstrike/packages/ui/src/components.
To finish setting up components, you will need to:
- manually reference the module by adding `mod components;` to your `main.rs` file
- add a reference to `asset!("/assets/dx-components-theme.css")` as a stylesheet in your app
```

`ui` doesn't have a `main.rs` but a `lib.rs`, wher eshould I add the theme? on every target (web, desktop and mobile)?