Overhaul of much of the page for clarification, updates, and to avoid duplication.

Fix formatting (triple backticks in 3 places).

Try again to fix triple backticks in the code block in "tar Archive of Completion Scripts for Manual Deployment".

Remove indentation in code block in bottom section, so that triple backticks create a fenced code block instead of being rendered.

Use correct paths to completions

Co-authored-by: Stanislav Zhuk <stasadev@gmail.com>

Use relative link to documentation

Co-authored-by: Stanislav Zhuk <stasadev@gmail.com>

Use relative link to documentation

Co-authored-by: Stanislav Zhuk <stasadev@gmail.com>

Use relative link to documentation

Co-authored-by: Stanislav Zhuk <stasadev@gmail.com>

Use relative link to documentation

Co-authored-by: Stanislav Zhuk <stasadev@gmail.com>

Use relative link to documentation

Co-authored-by: Stanislav Zhuk <stasadev@gmail.com>