Prettify docs-update.py

Remove commented code, use format for string concatenation, split long lines, fix how-to-run instructions
Signed-off-by: Davide Ceretti <dav.ceretti@gmail.com>
Add ENV variables support to WORKDIR build command

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
Docker-DCO-1.1-Signed-off-by: Adrien Folie <folie.adrien@gmail.com> (github: folieadrien)

Conflicts:
	builder/builder.go
		This file has been deleted.
Multiple fixes to the cli.md document.

*. Fixed headings so the side menu will now be consistent. Some sections
had H3s that were displaying and others did not leaving the left menu
very mismatched.

* Fixed several spelling errors.

* Re-formatted several long lines and badly laid out paragraphs.

* Fixed several double backticks.

* Added backticks to several outputs and variables.

* Removed two issues that are no longer valid.

* Removed several double spaces and extra lines.

Docker-DCO-1.1-Signed-off-by: James Turnbull <james@lovedthanlost.net> (github: jamtur01)
google: fix typo

Docker-DCO-1.1-Signed-off-by: Johan Euphrosine <proppy@google.com> (github: proppy)
Merge pull request #8426 from proppy/patch-12

google: fix typo
Merge pull request #8341 from unclejack/add_workdir_test

add test for workdir env vars and add docs
Merge pull request #8304 from davide-ceretti/chore/prettify-docs-update.py

Prettify docs-update.py
Merge pull request #8382 from jamtur01/cli

Multiple fixes to the cli.md document.
Extracting refactor from force-fully-qualified branch
Fixing unit tests