docs: R2D2 credentials as a prerequisite

docs/introduction/prerequisites.md

@@ -7,3 +7,13 @@
 - Required software, accounts, permissions, and external systems.
 - Supported Python, Cylc, and platform requirements.
 - Pre-installation checks for running Swell.
+
+## R2D2 credentials
+
+Most Swell experiments fetch observations and store backgrounds/analyses through
+[R2D2](r2d2_overview.md), so you'll need an R2D2 username and API key before you can run one.
+Set these up in `~/.swell/r2d2_credentials.yaml` as described in
+[R2D2 v3 credentials](../configuration_reference/r2d2_v3_credentials.md).
+
+If you don't have R2D2 credentials yet, you can still try Swell by passing `-k`/`--skip-r2d2` to
+`swell create` — see [QuickStart](quickstart.md#skipping-r2d2-for-a-first-run).

docs/introduction/quickstart.md

@@ -8,3 +8,16 @@
 - Create a maintained example experiment.
 - Launch and monitor the workflow.
 - Locate logs and verify the expected result.
+
+## Skipping R2D2 for a first run
+
+Are you new to Swell and don't have R2D2 credentials set up yet? Pass `-k`/`--skip-r2d2` to
+`swell create` to skip registering the experiment and storing products in R2D2:
+
+```bash
+swell create <suite> --skip-r2d2
+```
+
+This lets you complete a full create -> launch -> monitor cycle to see Swell working end to end
+before setting up your [R2D2 credentials](../configuration_reference/r2d2_v3_credentials.md). Tasks that use R2D2 (fetching observations, storing backgrounds/analyses) will be skipped rather
+than run.

docs/practical_examples/README.md

@@ -37,6 +37,13 @@ To see all available arguments use the command `swell create --help`.
  - **SLURM override:**
 It is possible to use the `-s` or `--slurm` option to modify (or override) SLURM directives for different models and each individual task. See [SLURM configuration](../configuration_reference/slurm_configuration.md) section for more details.
 
+- **Skipping R2D2:**
+  The `-k` or `--skip-r2d2` flag skips registering the experiment and storing products in R2D2. This is useful if you don't have [R2D2 credentials](../configuration_reference/r2d2_v3_credentials.md) configured yet, or want to run without touching R2D2 at all:
+
+   ```bash
+  swell create 3dvar_marine --skip-r2d2
+  ```
+
 - **Overriding** `experiment.yaml`**:**
   It is possible to override `experiment.yaml` keys using the override argument (`-o` or `--override`).
   For instance, to create a new experiment folder at a different location with a different id, use the override argument:

docs/running_an_experiment/creating_an_experiment.md

@@ -4,7 +4,7 @@ Once you have installed `swell` and configured `cylc` you should be able to crea
 
 A useful command when using swell is `swell --help`. This will take you through all the options within swell. The help traverses through the applications so you can similarly issue `swell create --help`
 
-- Make sure you've configured `~/.swell/r2d2_credentials.yaml` as described in [R2D2 v3 credentials](../configuration_reference/r2d2_v3_credentials.md).
+- Make sure you've configured `~/.swell/r2d2_credentials.yaml` as described in [R2D2 v3 credentials](../configuration_reference/r2d2_v3_credentials.md). If you don't have R2D2 credentials yet, you can skip this step and pass `-k`/`--skip-r2d2` to `swell create` instead.
 
 The first step is to create an experiment which is done with