Fix opus_gnome dataset card

I fixed a issue #4805.

I changed `"gnome"` to `"opus_gnome"` in[ README.md](https://github.com/huggingface/datasets/tree/main/datasets/opus_gnome#dataset-summary).

Fix #4805

Comments:
_The documentation is not available anymore as the PR was closed or merged._

@gojiteji why have you closed this PR and created an identical one?
- #4807 

@albertvillanova 
I forgot to follow "How to create a Pull" in CONTRIBUTING.md in this branch.

Both are identical. And you can push additional commits to this branch.

I see. Thank you for your comment.

Anyway, @gojiteji thanks for your contribution and this fix.

Once you have modified the `opus_gnome` dataset card, our Continuous Integration test suite performs some tests on it that make some additional requirements: the errors that appear have nothing to do with your contribution, but with these additional quality requirements.

> the errors that appear have nothing to do with your contribution, but with these additional quality requirements.

Is there anything I should do?

If you would like to address them as well in this PR, it would be awesome: https://github.com/huggingface/datasets/runs/7741104780?check_suite_focus=true


These are the 2 error messages:
```
E           ValueError: The following issues have been found in the dataset cards:
E           README Validation:
E           The following issues were found for the README at `/home/runner/work/datasets/datasets/datasets/opus_gnome/README.md`:
E           -	No first-level heading starting with `Dataset Card for` found in README. Skipping further validation for this README.

E           The following issues have been found in the dataset cards:
E           YAML tags:
E           Could not validate the metadata, found the following errors:
E           * field 'language':
E           	['ara', 'cat', 'foo', 'gr', 'nqo', 'tmp'] are not registered tags for 'language', reference at https://github.com/huggingface/datasets/tree/main/src/datasets/utils/resources/languages.json
```

In principle there are 2 errors:

The first one says, the title of the README does not start with `Dataset Card for`:
- The README title is: `# Dataset Card Creation Guide`
- According to the [template here](https://github.com/huggingface/datasets/blob/main/templates/README.md), it should be: `# Dataset Card for [Dataset Name]`

In relation with the languages:
- you should check whether the language codes are properly spelled
- and if so, adding them to our `languages.json` file, so that they are properly validated

Thank you for the detailed information. I'm checking it now.

```
E           ValueError: The following issues have been found in the dataset cards:
E           README Validation:
E           The following issues were found for the README at `/home/runner/work/datasets/datasets/datasets/opus_gnome/README.md`:
E           -	Expected some content in section `Data Instances` but it is empty.
E           -	Expected some content in section `Data Fields` but it is empty.
E           -	Expected some content in section `Data Splits` but it is empty.
```

I added `ara`, `cat`, `gr`, and `nqo` to  `languages.json` and removed `foo` and `tmp` from `README.md`.
I also write  Data Instances, Data Fields, and Data Splits in `README.md`.

Thanks for your investigation and fixes to the dataset card structure! I'm just making some suggestions before merging this PR: see below.

Should I create PR for `config.json` to add ` ara cat gr nqo` first?
I think I can pass this failing after that.

Or removing `ara, cat, gr, nqo, foo, tmp` from `README.md`. 

Once you address these issues, all the CI tests will pass.

Once the remaining changes are addressed (see unresolved above), we will be able to merge this:
- [ ] Remove "ara" from README
- [ ] Remove "cat" from README
- [ ] Remove "gr" from README
- [ ] Replace "tmp" with "tyj" in README
- [ ] Add "tyj" to `languages.json`:
  ```
  "tyj": "Tai Do; Tai Yo",

I did the five changes.