Add Parcels as submodule and source installation

Author: VeckoTheGecko

.gitignore

@@ -178,3 +178,9 @@ src/virtualship/_version_setup.py
 
 .vscode/
 .DS_Store
+
+# Ignore pixi.lock file for this project. The con of 22k lines of noise it adds to diffs is not worth
+# the minor benefit of perfectly reproducible environments for all developers (and all the tooling that would
+# be required to support that - see https://github.com/pydata/xarray/issues/10732#issuecomment-3327780806
+# for more details)
+pixi.lock

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "Parcels"]
+	path = Parcels
+	url = [email protected]:Parcels-code/Parcels.git

docs/contributing/index.md

@@ -18,7 +18,16 @@ To get started contributing to VirtualShip:
 
 **Step 2:** [Fork the repository](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/fork-a-repo#forking-a-repository)
 
-**Step 3:** Clone your fork and `cd` into the repository.
+**Step 3:** Clone your fork with submodules and `cd` into the repository.
+
+```bash
+git clone --recurse-submodules [email protected]:YOUR_USERNAME/virtualship.git
+cd virtualship
+```
+
+```{note}
+The `--recurse-submodules` flag is required to clone the Parcels submodule, which is used for testing and development.
+```
 
 **Step 4:** Install the Pixi environment
 

pixi.toml

@@ -28,7 +28,7 @@ pre-commit = { features = ["pre-commit"], no-default-feature = true }
 [dependencies] # keep section in sync with pyproject.toml dependencies
 python = ">=3.11"
 click = "*"
-parcels = ">3.1.0"
+parcels = {path="./Parcels"}
 pyproj = ">=3,<4"
 sortedcontainers = "==2.4.0"
 opensimplex = "==0.4.5"