Allow collaborators to self-assign issues (huggingface#2289)

* Support self-assign

* Updtate CONTRIBUTING with info about self-assign

* Set explicit numbers in ordered list elements

.github/workflows/self-assign.yaml

@@ -0,0 +1,16 @@
+name: Self-assign
+on:
+  issue_comment:
+    types: created
+jobs:
+  one:
+    runs-on: ubuntu-latest
+    if: >-
+      (github.event.comment.body == '#take' ||
+       github.event.comment.body == '#self-assign')
+      && !github.event.issue.assignee
+    steps:
+      - run: |
+          echo "Assigning issue ${{ github.event.issue.number }} to ${{ github.event.comment.user.login }}"
+          curl -H "Authorization: token ${{ secrets.GITHUB_TOKEN }}" -d '{"assignees": ["${{ github.event.comment.user.login }}"]}' https://api.github.com/repos/${{ github.repository }}/issues/${{ github.event.issue.number }}/assignees
+          curl -H "Authorization: token ${{ secrets.GITHUB_TOKEN }}" -X "DELETE" https://api.github.com/repos/${{ github.repository }}/issues/${{ github.event.issue.number }}/labels/help%20wanted

CONTRIBUTING.md

@@ -11,6 +11,19 @@ Many thanks in advance to every contributor.
 In order to facilitate healthy, constructive behavior in an open and inclusive community, we all respect and abide by 
 our [code of conduct](CODE_OF_CONDUCT.md).
 
+## How to work on an open Issue?
+You have the list of open Issues at: https://github.com/huggingface/datasets/issues
+
+Some of them may have the label `help wanted`: that means that any contributor is welcomed!
+
+If you would like to work on any of the open Issues:
+
+1. Make sure it is not already assigned to someone else. You have the assignee (if any) on the top of the right column of the Issue page.
+
+2. You can self-assign it by commenting on the Issue page with one of the keywords: `#take` or `#self-assign`.
+
+3. Work on your self-assigned issue and eventually create a Pull Request.
+
 ## How to create a Pull Request?
 1. Fork the [repository](https://github.com/huggingface/datasets) by clicking on the 'Fork' button on the repository's page. This creates a copy of the code under your GitHub user account.