add metrec: arabic poetry dataset
@lhoestq removed prints and added the dataset card.  @lhoestq, I want to add other datasets as well. I am not sure if it is possible to do so with the same branch.  Hi @zaidalyafeai, really excited to get more Arabic coverage in the lib, thanks for your contribution!

Couple of last comments:
- this PR seems to modify some files that are unrelated to your dataset. Could you rebase from master? It should take care of that.
- The dataset card is a good start! Can you describe the task in a few words and add more information in the Data Structure part, including listing and describing the fields? Also, if you don't know how to fill out a paragraph, or if you have some information but think more would be beneficial, please leave `[More Information Needed]` instead of `[N/A]` > Hi @zaidalyafeai, really excited to get more Arabic coverage in the lib, thanks for your contribution!
> 
> Couple of last comments:
> 
> * this PR seems to modify some files that are unrelated to your dataset. Could you rebase from master? It should take care of that.
> * The dataset card is a good start! Can you describe the task in a few words and add more information in the Data Structure part, including listing and describing the fields? Also, if you don't know how to fill out a paragraph, or if you have some information but think more would be beneficial, please leave `[More Information Needed]` instead of `[N/A]`

I have no idea how some other files changed. I tried to rebase and push but this created some errors. I had to run the command 
`git push -u --force origin add-metrec-dataset` which might cause some problems.  Feel free to create another branch/another PR without all the other changes @yjernite can you explain which other files are changed because of the PR ? https://github.com/huggingface/datasets/pull/893/files only shows files related to the dataset.  Right ! github is nice with us today :) Looks like this one is ready to merge, thanks @zaidalyafeai ! @lhoestq thanks for the merge. I am not a GitHub geek. I already have another dataset to add. I'm not sure how to add another given my forked repo. Do I  follow the same steps with a different checkout name ? If you've followed the instructions in here : https://github.com/huggingface/datasets/blob/master/ADD_NEW_DATASET.md#start-by-preparing-your-environment

(especially point 2. and the command `git remote add upstream ....`)

Then you can try
```
git checkout master
git fetch upstream
git rebase upstream/master
git checkout -b add-<my-new-dataset-name>
```