Fix broken GitHub Actions workflows (#402)

* Fix pull-request-labeler to permit outside collaborator

* Add welcome GitHub workflow

* Update welcome.yaml

.github/workflows/pull-request-labeler.yaml

@@ -1,7 +1,7 @@
 name: Label Pull Requests
 
 on:
-- pull_request
+- pull_request_target
 
 jobs:
   label-pr:

.github/workflows/welcome.yaml

@@ -0,0 +1,27 @@
+name: Welcome for First Issue or Pull Request
+
+on:
+  pull_request_target:
+    types:
+    - opened
+  issues:
+    types:
+    - opened
+
+jobs:
+  welcome:
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Welcome for First Issue or Pull Request
+      uses: actions/first-interaction@v1
+      with:
+        repo-token: ${{ secrets.GITHUB_TOKEN }}
+        issue-message: |
+          ### :wave: Welcome! Looks like this is your first issue.
+
+          Hey, thanks for your contribution! Please give us a bit of time to review it. 😄
+        pr-message: |
+          ### :wave: Welcome! Looks like this is your first pull request.
+
+          Hey, thanks for your contribution! Please give us a bit of time to review it. 😄