Update notebook

Author: maxrjones

docs/user-guide/examples/rectilinear_chunks.ipynb

@@ -2,7 +2,7 @@
  "cells": [
   {
    "cell_type": "code",
-   "execution_count": 1,
+   "execution_count": null,
    "id": "da9139cc",
    "metadata": {
     "execution": {
@@ -28,7 +28,7 @@
     "# ]\n",
     "#\n",
     "# [tool.uv.sources]\n",
-    "# zarr = { git = \"https://github.com/maxrjones/zarr-python\", branch = \"poc/unified-chunk-grid\" }\n",
+    "# zarr = { git = \"https://github.com/zarr-developers/zarr-python\", branch = \"main\" }\n",
     "# xarray = { git = \"https://github.com/maxrjones/xarray\", branch = \"poc/unified-zarr-chunk-grid\" }\n",
     "# ///"
    ]
@@ -42,6 +42,8 @@
     "\n",
     "This notebook demonstrates the unified chunk grid implementation from [#3802](https://github.com/zarr-developers/zarr-python/pull/3802), which adds support for rectilinear (variable) chunk grids.\n",
     "\n",
+    "Note that it requires installing from a fork of Xarray; this will ideally be incorporated in the codebase and included in a future Xarray release.\n",
+    "\n",
     "Rectilinear grids allow different chunk sizes along each dimension, which is useful for data that doesn't partition evenly. For example, sparse HEALPix cells grouped by parent tile, boundary-padded HPC arrays, or ingesting existing variable-chunked datasets via VirtualiZarr."
    ]
   },