Substantial rewrite of the Cookbook guide (ProjectPythia#435)

* Substantial rewrite of the guide

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* fix typo

Co-authored-by: clyne <[email protected]>

* Update portal/cookbook-guide.md

Co-authored-by: Robert Ford <[email protected]>

* Add lines between major sections

* Remove invisible lines

* clarify pages setting

Co-authored-by: clyne <[email protected]>

* clarify build command instruction

Co-authored-by: clyne <[email protected]>

* Clarifications after Clyne review

* Add note about workflows not running on forks

* Add more guidance on PRs and previews

* clarification about missing gh-pages checkbox

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: clyne <[email protected]>
Co-authored-by: Robert Ford <[email protected]>

Author: 4 people