Add info on link_task_source to docs

docs/web/docs/guides/tutorials/custom_react.md

@@ -36,15 +36,30 @@ mephisto:
     task_tags: "test,simple,button"
 ```
 
-The only change we'll make is to the `task_name` (as you should on any new tasks!), but we will update the other fields as we go. It's important to note the `task_source` and `extra_source_dir` arguments though, as this is where the `StaticReactBlueprint` class will be looking for the compiled React app's Javascript bundle as well as a folder for extra static resources for the page, respectively.
+It is important to give a new `task_name` as we are creating a custom task. For local development **only** it also makes sense to set `link_task_source` to true. This allows changes to propagate to your localhost server when you reload the page (otherwise you would have to shutdown and restart the server to see changes). 
+
+The `task_source` and `extra_source_dir` arguments are also of importance, as this is where the `StaticReactBlueprint` class will be looking for the compiled React app's Javascript bundle as well as a folder for extra static resources for the page, respectively.
 
 ### 1.2 Launching the task
 From the current directory, you should be able to execute the run script and get a job working. We're using a different `task_name` to prevent polluting our later task with data that won't share the same format. It is a good practice to do this with initial iterations, and to change the `task_name` any time you change input or output arguments.
+
+You can update the `task_name` and `link_task_source` values in your config and run the task like below
 ```bash
-python run_task.py mephisto.task.task_name=custom-react-tutorial-iterating
+python run_task.py
+```
+
+or you can set them when you run the task:
+
+```bash
+python run_task.py mephisto.task.task_name=custom-react-tutorial-iterating mephisto.blueprint.link_task_source=true
 ```
 This will launch a simple task where an annotator is supposed to note a sentence as being good or bad. Clicking a button auto-submits the task. In the next sections we'll add other content. 
 
+To establish a link where your changes will be propagated to the localhost server(when you reload), create a separate terminal window and run
+```bash
+cd webapp && npm run dev:watch
+```
+
 Moving forward, we'll update this task so that workers are able to edit the text as well as rate the original sentence.
 
 ## 2. Providing new data to the task

mephisto/operations/operator.py

@@ -313,7 +313,7 @@ def launch_task_run_or_die(
             raise e
 
         live_run.task_launcher.create_assignments()
-        live_run.task_launcher.launch_units(task_url)
+        live_run.task_launcher.launch_units(url=task_url, run_config=run_config)
 
         self._task_runs_tracked[task_run.db_id] = live_run
         task_run.update_completion_progress(status=False)

mephisto/operations/task_launcher.py

@@ -26,7 +26,7 @@
 if TYPE_CHECKING:
     from mephisto.data_model.task_run import TaskRun
     from mephisto.abstractions.database import MephistoDB
-
+from omegaconf import DictConfig, OmegaConf
 import threading
 from mephisto.utils.logger_core import get_logger
 import types
@@ -180,7 +180,7 @@ def generate_units(self):
             if not self.unlaunched_units:
                 break
 
-    def _launch_limited_units(self, url: str) -> None:
+    def _launch_limited_units(self, url: str, run_config: Optional[DictConfig]) -> None:
         """use units' generator to launch limited number of units according to (max_num_concurrent_units)"""
         # Continue launching if we haven't pulled the plug, so long as there are currently
         # units to launch, or more may come in the future.
@@ -191,15 +191,24 @@ def _launch_limited_units(self, url: str) -> None:
                 if unit is None:
                     break
                 unit.launch(url)
+            if (
+                run_config is not None
+                and run_config.blueprint.link_task_source == False
+            ):
+                logger.info(
+                    "If you want your server to update on reload whenever you make changes to your webapp, then make sure to set \n\nlink_task_source: true\n\nin your task's hydra configuration and run \n\ncd webapp && npm run dev:watch\n\nin a separate terminal window. For more information check out:\nhttps://mephisto.ai/docs/guides/tutorials/custom_react/#12-launching-the-task"
+                )
             if self.generator_type == GeneratorType.NONE:
                 break
         self.finished_generators = True
 
-    def launch_units(self, url: str) -> None:
+    def launch_units(self, url: str, run_config: Optional[DictConfig]) -> None:
         """launch any units registered by this TaskLauncher"""
         self.launch_url = url
         self.units_thread = threading.Thread(
-            target=self._launch_limited_units, args=(url,), name="unit-generator"
+            target=self._launch_limited_units,
+            args=(url, run_config),
+            name="unit-generator",
         )
         self.units_thread.start()