Remove duplicate docs link
Remove unnecessary HTML comments
s/Github/GitHub/
Remove GitHub buttons which sadly don't work over https
Move scripts to bottom
Remove line numbers from <pre> which have various problems

They're smashed up against the text, look odd when the text wraps, and
don't work when there's only one line. There's also an extra line
number at the end if the <pre> tag has a trailing newline.

The line numbers aren't necessary, so it's easier to remove them than
fix them.