added greetings automation

Author: mikecentola

.github/workflows/greetings.yml

@@ -0,0 +1,20 @@
+name: Greetings
+
+on: [pull_request_target, 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: 'Hello and welcome! Thanks for creating your first issue! Someone from our community will get back to you soon!'
+          pr-message: >
+            Thanks for opening your first pull reqest in VSCode G-Code Syntax!
+            
+            Please make sure you read the [Contributing Guide](https://github.com/appliedengdesign/vscode-gcode-syntax/blob/master/CONTRIBUTING.md) and follow the [Code of Conduct](https://github.com/appliedengdesign/vscode-gcode-syntax/blob/master/CODE_OF_CONDUCT.md).