Add better documentation, trigger namedtuple.

recipe_modules/step/example.expected/invalid_access.json

 [
   {
     "cmd": [
       "echo",
       "Hello World"
     ],
     "name": "hello"
   },
   {
     "cmd": [
@@ skipping 38 matching lines @@
     ],
     "name": "hello (3)",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@the reason@The reason@@@",
       "@@@STEP_LOG_LINE@the reason@it failed@@@",
       "@@@STEP_LOG_END@the reason@@@",
       "@@@STEP_EXCEPTION@@@"
     ]
   },
   {
+    "cmd": [],
     "name": "Just print stuff",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@more@More stuff@@@",
       "@@@STEP_LOG_END@more@@@"
     ]
   },
   {
     "cmd": [
       "echo",
       "goodbye"
@@ skipping 49 matching lines @@
       "nothing"
     ],
     "name": "no-op"
   },
   {
     "name": "$result",
     "reason": "Invalid Step Data Access: StepDataAttributeError('The recipe attempted to access missing step data \"json\" for step \"no-op\". Please examine that step for errors.',)",
     "status_code": -1
   }
 ]