move computation notebooks to be in a dedicated section

Author: TomNicholas

_toc.yml

@@ -38,7 +38,10 @@ parts:
 
   - caption: Intermediate
     chapters:
-      - file: intermediate/01-high-level-computation-patterns
+      - file: intermediate/computation/index
+        sections:
+          - file: intermediate/01-high-level-computation-patterns.ipynb
+          - file: intermediate/hierarchical-computation.ipynb
       - file: intermediate/indexing/indexing
         sections:
           - file: intermediate/indexing/advanced-indexing.ipynb

intermediate/01-high-level-computation-patterns.ipynb renamed to intermediate/computation/01-high-level-computation-patterns.ipynb

@@ -0,0 +1,5 @@
+# Computations
+
+```{tableofcontents}
+
+```

intermediate/hierarchical_computation.ipynb renamed to intermediate/computation/hierarchical_computation.ipynb

@@ -41,7 +41,7 @@
     "| Introduction and Setup | 1:30 (10 min) | | \n",
     "| The Xarray Data Model | 1:40 (50 min) | [Data structures](../../fundamentals/01_data_structures.md) | \n",
     "| *10 minute Break*  \n",
-    "| Computational Patterns | 2:30 (50 min) |  [Computational Patterns](../../intermediate/01-high-level-computation-patterns.ipynb) <br> [Hierarchical computation](../../intermediate/hierarchical-computation.ipynb) |  \n",
+    "| Computational Patterns | 2:30 (50 min) |  [Computational Patterns](../../intermediate/computation/01-high-level-computation-patterns.ipynb) <br> [Hierarchical computation](../../intermediate/computation/hierarchical-computation.ipynb) |  \n",
     "| *10 minute Break*  | \n",
     "| Zarr & the cloud | 4:30 (50 min)  | [Intro to Zarr](../../intermediate/intro-to-zarr.ipynb) <br> [CMIP6 on the cloud](../../intermediate/remote_data/cmip6-cloud.ipynb) <br> |\n",
     "| *10 minute Break*  | \n",