Add gdu
Add gdu

**Please provide package links to:**

- repo link (github.com, gitlab.com, etc): https://github.com/dundee/gdu
- pkg.go.dev: https://pkg.go.dev/github.com/dundee/gdu
- goreportcard.com: https://goreportcard.com/report/github.com/dundee/gdu
- coverage service link ([codecov](https://codecov.io/), [coveralls](https://coveralls.io/), [gocover](http://gocover.io/) etc.): https://coveralls.io/github/dundee/gdu?branch=master

Very good coverage

**Note**: _that new categories can be added only when there are 3 packages or more._

**Make sure that you've checked the boxes below before you submit PR:**
_not every repository (project) will fit into every option, but most projects should_

- [x] I have added my package in alphabetical order.
- [x] I have an appropriate description with correct grammar.
- [x] I know that this package was not listed before.
- [x] I have added pkg.go.dev link to the repo and to my pull request.
- [x] I have added coverage service link to the repo and to my pull request.
- [x] I have added goreportcard link to the repo and to my pull request.
- [x] I have read [Contribution guidelines](https://github.com/avelino/awesome-go/blob/master/CONTRIBUTING.md#contribution-guidelines), [maintainers note](https://github.com/avelino/awesome-go/blob/master/CONTRIBUTING.md#maintainers) and [Quality standard](https://github.com/avelino/awesome-go/blob/master/CONTRIBUTING.md#quality-standards).

Thanks for your PR, you're awesome! :+1:
pconcepcion/awesome-go,theckman/awesome-go,sadlil/awesome-go,jmelfi/awesome-go,avelino/awesome-go