Add Mermaid build diagram

Author: hsutter

docs/index.md

@@ -1,6 +1,12 @@
 
 # Overview: What are Cpp2 and cppfront? How do I get and build cppfront?
 
+``` cpp title="hello.cpp2"
+main: () = {
+    std::cout << "Hello, world!\n";
+}
+```
+
 ## What is Cpp2?
 
 "Cpp2," short for "C++ syntax 2," is my ([Herb Sutter's](https://github.com/hsutter)) personal project to try to make writing ordinary C++ types/functions/objects be much **simpler and safer**, without breaking backward compatibility. Bjarne Stroustrup said it best:

docs/welcome/hello-world.md

@@ -1,5 +1,20 @@
 # **Hello, world!**
 
+<table><tr><td>
+``` cpp title="hello.cpp2"
+main: () = {
+    std::cout << "Hello, world!\n";
+}
+```
+</td><td>
+``` mermaid
+graph TB
+  A[hello.cpp2] ==> B([cppfront]);
+  B ==> C[hello.cpp];
+  C ==> D([Your favorite C++ compiler]);
+```
+</td></tr></table>
+
 ## A `hello.cpp2` program
 
 Here is the usual one-line starter program that prints `Hello, world!`. Note that this is a complete program, no `#!cpp #include` required:

mkdocs.yml

@@ -80,7 +80,11 @@ markdown_extensions:
       generic: true
   - footnotes
   - pymdownx.details
-  - pymdownx.superfences
+  - pymdownx.superfences:
+      custom_fences:
+        - name: mermaid
+          class: mermaid
+          format: !!python/name:pymdownx.superfences.fence_code_format
   - pymdownx.mark
   - attr_list