Toastr: Can't follow steps from document written

### Issue type

**I'm submitting a ...** (check one with "x")

* [X] bug report
* [ ] feature request

### Issue description

**Current behavior:**

When I try to follow the steps to use custom toastr of Nebular 4 version in my angular app. I think the document is not properly written step by step.
**Expected behavior:**

When I import service and use module in appmodule file. After that what I have to do in my component to use toastr?
**Steps to reproduce:**

i have followed all the steps from Document, It does nothing
**Related code:**

```
insert short code snippets here
```

### Other information:

**npm, node, OS, Browser**
```

```
All the latest versions of Angular , Nodejs, Nebular, Npm
**Angular, Nebular**
```

```