added first pr action - checklists

Author: gregsdennis

.github/workflows/checklist.md

@@ -0,0 +1,3 @@
+- [ ] [Issue](https://github.com/json-schema-org/json-schema-spec/issues) linked
+- [ ] [Milestone](https://github.com/json-schema-org/json-schema-spec/milestones) assigned
+- [ ] Test coverage issue in [test suite](https://github.com/json-schema-org/JSON-Schema-Test-Suite)

.github/workflows/checklist.yml

@@ -0,0 +1,21 @@
+name: Checklist Handler
+on: [pull_request]
+
+jobs:
+  label:
+    runs-on: ubuntu-latest
+    steps:
+      - id: get-comment-body
+        run: |
+          body=$(cat checklist.md)
+          body="${body//'%'/'%25'}"
+          body="${body//$'\n'/'%0A'}"
+          body="${body//$'\r'/'%0D'}" 
+          echo ::set-output name=body::$body
+      - name: Update comment
+        uses: peter-evans/create-or-update-comment@v1
+        with:
+          comment-id: ${{ github.event.comment.id }}
+          body: ${{ steps.get-comment-body.outputs.body }}
+          token: GITHUB_TOKEN
+          edit-mode: append