Apply many fixes re formatting of the document:
- Remove unnecessary quotation marks,
- Use ``backticks`` for inline code formatting,
- Fix incorrect break of a long TEMPLATECONF=.. line,
- Remove unnecessary break of `wget ...` line,
- Add/remove some spaces,
- Use ``#`` for comments in shell commands,
- Make GPIO capitalization consistent.

Signed-off-by: Wojciech Zmuda <wojciech.zmuda@huawei.com>