Add Workflow to run Shellcheck

.github/workflows/shellcheck.yml

@@ -0,0 +1,15 @@
+name: Shellcheck
+
+on: push
+
+jobs:
+  shellcheck:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v1
+
+    - name: Install shellcheck
+      run: apt-get install shellcheck
+
+    - name: Run shellcheck
+      run: shellcheck *.sh