[Documentation][zos_script] Add and standarize docstrings on modules/zos_script.py (#1390)

* Add and standarize docstrings on module-utils/zos_script.py

* Add changelog fragment

Author: IsaacVRey

changelogs/fragments/1390-update-docstring-zos_script.yml

@@ -0,0 +1,3 @@
+trivial:
+  - zos_script - Updated docstrings to numpy style for visual aid to developers.
+    (https://github.com/ansible-collections/ibm_zos_core/pull/1390).

plugins/modules/zos_script.py

@@ -229,6 +229,17 @@
 
 
 def run_module():
+    """Initialize module.
+
+    Raises
+    ------
+    fail_json
+        Parameter verification failed.
+    fail_json
+        The given chdir does not exist on the system.
+    fail_json
+        The script terminated with an error.
+    """
     module = AnsibleModule(
         argument_spec=dict(
             chdir=dict(type='str', required=False),