post review edits

Author: j-atkins

docs/user-guide/assignments/Sail_the_ship.ipynb

@@ -157,7 +157,7 @@
     "The next step is to finalise the expedition schedule plan, including setting times and instrument selection choices for each waypoint, as well as configuring the ship (including any underway measurement instruments). \n",
     "\n",
     "<div class=\"alert alert-block alert-info\"> \n",
-    "**NOTE**: This section describes the process of finalising the expedition schedule and instrument selection using the `virtualship plan` application. This is the recommended way for most users but when expeditions become larger with many waypoints, it can become cumbersome to use the planning tool (note, using VirtualShip in a remote terminal / cloud-based environment can also introduce lag in the user-interface). **In this case, you may prefer to edit the** `expedition.yaml` **file directly (see [here](../tutorials/working_with_expedition_yaml.md) for more details on how to do so)**.\n",
+    "**NOTE**: This section describes the process of finalising the expedition schedule and instrument selection using the `virtualship plan` application. For expeditions with many waypoints, it can become cumbersome to use the planning tool (note, using VirtualShip in a remote terminal / cloud-based environment can also introduce lag in the user-interface). **In this case, you may prefer to edit the** `expedition.yaml` **file directly (see [here](../tutorials/working_with_expedition_yaml.md) for more details on how to do so)**.\n",
     "</div>\n",
     "\n",
     "\n",

docs/user-guide/tutorials/working_with_expedition_yaml.md

@@ -4,7 +4,7 @@ This tutorial will guide you through the structure of the `expedition.yaml` file
 
 The `expedition.yaml` file is ingested by `virtualship run` and is used to configure expeditions. It contains metadata and settings that define the parameters of an expedition, including information about ship speed, instrument configurations, waypoint timings and instrument selections.
 
-This tutorial describes an alternative means to using the `virtualship plan` command, which provides a user-friendly interface for interacting with `expedition.yaml` but can become cumbersome for long, complex expeditions with many waypoints and instruments. Interacting with the `expedition.yaml` file directly tends to be faster for larger expeditions.
+This tutorial describes an alternative means to using the `virtualship plan` command, which provides a user-friendly interface for interacting with `expedition.yaml` but can become cumbersome for long, complex expeditions with many waypoints and instruments. Interacting with the `expedition.yaml` file directly tends to be faster for larger expeditions and experienced users.
 
 ### Editing the file
 
@@ -72,7 +72,7 @@ In the example above, some instrument configuration parameters are replaced by e
 
 This section contains a list of `waypoints` that define the expedition's route. Each waypoint includes:
 
-- **Instruments (`instrument`)**: A list of instruments to be deployed at that waypoint. Add or remove instruments by adding or deleting entries on _new lines_.
+- **Instruments (`instrument`)**: A list of instruments to be deployed at that waypoint. Add or remove instruments by adding or deleting entries on _new lines_. The instrument selection can also be left empty (i.e., no instruments deployed at that waypoint) by setting the parameter to: `instrument: null`.
 
 ```{tip}
 Full list of instruments supported for deployment at waypoints (case-sensitive): `CTD`, `CTD_BGC`, `DRIFTER`, `ARGO_FLOAT`, `XBT`.