Add new workflow for greetings

Add a new workflow to be welcome our new contributors and let them know how to find help.

.github/workflows/greetings.yml

@@ -0,0 +1,22 @@
+name: Greetings
+
+on: [pull_request, issues]
+
+jobs:
+  greeting:
+    runs-on: ubuntu-latest
+    permissions:
+      issues: write
+      pull-requests: write
+    steps:
+    - uses: actions/first-interaction@v1
+      with:
+        repo-token: ${{ secrets.GITHUB_TOKEN }}
+        issue-message: |
+          Thank you for reporting your first issue! Be sure that we will be looking at it.
+          Please let the maintainers know if your issue has not got enough attention after a few days.
+          If any doubt, please consult our issue [tutorial](https://github.com/gophercloud/gophercloud/blob/master/docs/contributor-tutorial/step-02-issues.md).
+        pr-message: |
+          Thank you for reporting your first PR! Be sure that we will be looking at it.
+          Please let the maintainers know if your PR has not got enough attention after a few days.
+          If any doubt, please consult our PR [tutorial](https://github.com/gophercloud/gophercloud/blob/master/docs/contributor-tutorial/step-05-pull-requests.md).