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.

2018/ferguson/README.md

@@ -28,7 +28,7 @@ make
 make test
 ```
 
-### Alternate code:
+## Alternate code:
 
 The author provided an alternate version which has a simpler keyboard for the
 monkey Eric. See his comments under the 'keyboards' section, briefly referred to