Changing heading level of 'Alternate code'

Change level 3 (###) to level 2 (##):

    sgit -e 's/^### \(Alternate code\)/## \1/g' '*README.md'

which is the same as:

    sgit -e 's/^### Alternate code/## Alternate code/g' '*README.md'

This is per discussion in GitHub.

2020/endoh3/README.md

@@ -23,7 +23,7 @@ make
 # And watch closely for 15-20 seconds
 ```
 
-### Alternate code:
+## Alternate code:
 
 An alternate version of this entry, `prog.alt.c`, is provided.  This alternate code uses Unicode letters.