Include demo graph from g-adopt repository

This is a mermaid.js diagram that we include as a snippet, allowing
for more dynamic configuration of the relationship between demos.

.github/workflows/build.yml

@@ -45,6 +45,7 @@ jobs:
           rm -rf rendered && mkdir rendered
           find tutorials/demos -name '*.ipynb' -exec cp "{}" rendered \;
           cp tutorials/demos/.pages rendered
+          cp tutorials/demos/.diagram.mermaid rendered
         env:
           GADOPT_LOGLEVEL: WARN
       - uses: actions/upload-artifact@v4

docs/tutorials/index.md

@@ -4,7 +4,9 @@ The diagram below shows several G-ADOPT example codes and how they
 relate to each other.  These notebooks demonstrate how to use G-ADOPT
 to set up (forward and inverse) geodynamical simulations.
 
-INCLUDE IMAGE HERE.
+```mermaid
+--8<-- "docs/tutorials/.diagram.mermaid"
+```
 
 We start with the most basic problem - isoviscous, incompressible
 convection, in an enclosed 2-D Cartesian box (base) - and

mkdocs.yml

@@ -21,7 +21,11 @@ markdown_extensions:
   - md_in_html
   - pymdownx.details
   - pymdownx.snippets
-  - pymdownx.superfences
+  - pymdownx.superfences:
+      custom_fences:
+        - name: mermaid
+          class: mermaid
+          format: !!python/name:pymdownx.superfences.fence_code_format
   - toc:
       toc_depth: 3
 extra_css: