Add workflow to greet first-time contributors (#376)

Author: mhucka

.github/workflows/first-interaction.yaml

@@ -0,0 +1,74 @@
+# Summary: add a welcoming comment to first-time contributors' issues & PRs.
+# This is written in a generic way so that we can use the same workflow
+# in all our quantumlib repos.
+# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+name: Welcome first interactions
+run-name: Welcome ${{github.actor}}'s first interaction
+
+on:
+  issues:
+    types: [opened]
+  pull_request:
+    types: [opened]
+
+# Declare default permissions as read-only.
+permissions: read-all
+
+jobs:
+  welcome:
+    name: Check for first interaction
+    runs-on: ubuntu-24.04
+    timeout-minutes: 10
+    permissions:
+      issues: write
+      pull-requests: write
+    env:
+      repo: ${{github.server_url}}/${{github.repository}}
+      files: ${{github.server_url}}/${{github.repository}}/blob/${{github.ref_name}}
+    steps:
+      - name: Add a welcome comment if appropriate
+        uses: actions/first-interaction@2ec0f0fd78838633cd1c1342e4536d49ef72be54 # v1.3.0
+        with:
+          repo-token: ${{secrets.GITHUB_TOKEN}}
+          issue-message: |
+            Hello and welcome, ${{github.actor}} 👋!
+
+            Thanks for filing your first issue with the ${{github.repository}}
+            project! Here are some quick tips:
+
+            - Please make sure to read our [community participation
+            guidelines](${{env.files}}/CODE_OF_CONDUCT.md).
+
+            - If this is a bug report, we'll probably need the following
+            details in order to diagnose the issue. If they're not in the
+            original issue description, please consider adding them now:
+
+               - [ ] Environment you are using (MacOS, Windows, Colab, etc.)
+               - [ ] Version of Python you are using
+               - [ ] Steps to reproduce the issue
+
+            - Please look through [existing issues](${{env.repo}}/issues) for
+            any that look the same as this one. If you find a similar issue,
+            consider closing this one; if you don't want to close this one, can
+            you explain how this new one differs from the other one?
+          pr-message: |
+            Hello and welcome, ${{github.actor}} 👋!
+
+            Thanks for making your first pull request to the
+            ${{github.repository}} project! Here are some quick tips:
+
+            - Please make sure to read the [contributing
+            guide](${{env.files}}/CONTRIBUTING.md) and [community participation
+            guidelines](${{env.files}}/CODE_OF_CONDUCT.md).
+
+            - All contributors must sign the [Contributor License
+            Agreement](https://cla.developers.google.com/about) (CLA). If
+            [googlebot](https://github.com/googlebot) leaves a comment on this
+            pull request, make sure you follow the instructions it provides.
+
+            - If this pull request fixes a bug, please reference the relevant
+            issue number in the [issue tracker](${{env.repo}}/issues).
+
+            Please allow time for the project community to be able to read and
+            evaluate your pull request. Thanks again!