added shellcheck workflow

Author: sdushantha

.github/workflows/main.yml

@@ -0,0 +1,23 @@
+# This is a basic workflow to help you get started with Actions
+
+name: Shellcheck
+
+# Triggers the workflow on push or pull request on all branches
+on: [push, pull_request]
+
+# A workflow run is made up of one or more jobs that can run sequentially or in parallel
+jobs:
+  # This workflow contains a single job called "build"
+  build:
+    # The type of runner that the job will run on
+    runs-on: ubuntu-latest
+
+    # Steps represent a sequence of tasks that will be executed as part of the job
+    steps:
+      # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
+      - uses: actions/checkout@v2
+
+      # Runs a set of commands using the runners shell
+      - name: Run shellcheck
+        run: |
+          shellcheck -s sh tmpsms