CI: Adding GitHub action to assign issues based on comment

.github/workflows/assign.yml

@@ -0,0 +1,15 @@
+name: Assign
+on:
+  issue_comment:
+    types: created
+
+jobs:
+  one:
+    runs-on: ubuntu-latest
+    steps:
+      - name:
+        run: |
+            if [[ "${{ github.event.comment.body }}" == "take" ]]; then
+                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
+            fi

doc/source/development/contributing.rst

@@ -24,6 +24,27 @@ and `good first issue
 where you could start out. Once you've found an interesting issue, you can
 return here to get your development environment setup.
 
+When you start working on an issue, it's a good idea to assign the issue to yourself,
+so nobody else duplicates the work on it. GitHub restricts assigning issues to maintainers
+of the project only. In most projects, and until recently in pandas, contributors added a
+comment letting others know they are working on an issue. While this is ok, you need to
+check each issue individually, and it's not possible to find the unassigned ones.
+
+For this reason, we implemented a workaround consisting of adding a comment with the exact
+text `take`. When you do it, a GitHub action will automatically assign you the issue
+(this will take seconds, and may require refreshint the page to see it).
+By doing this, it's possible to filter the list of issues and find only the unassigned ones.
+
+So, a good way to find an issue to start contributing to pandas is to check the list of
+`unassigned good first issues <https://github.com/pandas-dev/pandas/issues?q=is%3Aopen+is%3Aissue+label%3A%22good+first+issue%22+no%3Aassignee>`_
+and assign yourself one you like by writing a comment with the exact text `take`.
+
+If for whatever reason you are not able to continue working with the issue, please try to
+unassign it, so other people know it's available again. You can check the list of
+assigned issues, since people may not be working in them anymore. If you want to work on one
+that is assigned, feel free to kindly ask the current assignee if you can take it
+(please allow at least a week of inactivity before considering work in the issue discontinued).
+
 Feel free to ask questions on the `mailing list
 <https://groups.google.com/forum/?fromgroups#!forum/pydata>`_ or on `Gitter`_.