Update docs

• Update README.rst

  • Don't nest code blocks inside quote blocks.
  • Replace bash with sh, as there's nothing bash-specific in the examples.
  • There is no syntax highlighting for grub, use sh.
  • Use sentence case for headings.
  • Use monospace for paths.

• Update README.profile.rst

  • Move to docs/.
  • Don't nest code blocks inside quote blocks.
  • Use monospace for paths, options, values, etc.

• Remove docs/README.build. Superseded by README.rst

• Remove docs/README.knownissues. Replaced by issue #83 (moved).