Added pipeline step for checking all shell scripts in the repo

Drone.md

@@ -12,3 +12,13 @@ steps:
     commands:
       - "shellcheck testScript.sh"
 ```
+
+To check all .sh files in the repo:
+
+```yaml
+steps:
+  - name: shellcheck
+    image: koalaman/shellcheck-alpine:stable
+    commands:
+      - "find . -name *.sh -exec shellcheck {} +"
+```