Clean up readme

From top to bottom:

1. Drop the leading `===`. It is interpreted as an `<hl>`.
2. Wrap the ordered list at 80 chars and tweak its prose.
3. Drop leading tab and hash from all code samples. Fenced code blocks (denoted
   by triple-backticks) do not require any tabbing. The hash mark is a
   convention that indicates a command needs to be run as root, and it appears
   to be unnecessary in most or all cases.
4. Use single backticks to denote inline code. Using triple backticks for inline
   code is syntactically incorrect.
5. Add a blank line after the "code contribution" header, for the sake of
   consistency and niceness.