docs: guide for porting an html site to gatsby (#18609)

* docs: guide for porting part of a html site to gatsby

* fix: add missing normalize.css file to trees, build sentence rewrite

* fix: change links to be relative paths

* Apply suggestions from code review

Co-Authored-By: Kyle Gill <[email protected]>

* Apply suggestions from @gillkyle code review

* Clearer and Consistenter(heh) prefix descriptions

* format is aggressive about wrapping here, switching to start/end marks!

* bracket typo, square the curl

* Apply suggestions from code review

Co-Authored-By: Michael <[email protected]>

* parting more ports and the complete Gatsby section, per @muescha suggestion

* Update docs/docs/porting-part-of-a-html-site-to-gatsby.md

Co-Authored-By: Michael <[email protected]>

* Make page more general, for porting part and the whole

Co-Authored-By: Marcy Sutton <[email protected]>

* Apply suggestions from code review

Co-Authored-By: Marcy Sutton <[email protected]>

* Style guide: less we more you

Co-Authored-By: Marcy Sutton <[email protected]>

* Apply suggestions from code review

- Briefly explain JSX and add in some mentions.
- Expand and clarify JavaScript / JSX passages.

Co-Authored-By: Marcy Sutton <[email protected]>

* Review: Clarify tooling and building points.

Co-Authored-By: Marcy Sutton <[email protected]>

* condense why section and link off to core philosophy

* expand on isolation -> integration in porting process

* add file example for adjusting Link tags in porting more parts

* fix heading structure: add h1 on each page and make logo a styled anchor

* change name to match new title

* update sidebar and breadcrumb titles

* remove assetPrefix from example project, add link as note

* restructure for full html site port, with note for prefix options

* fix out of date directory name

* correct contradicting sentence about not changing copied over html markup

* expand opening to position guide relative to main tutorial

* Apply suggestions from code review

Co-Authored-By: Marcy Sutton <[email protected]>

* fix gatsby-site path roots

* Apply suggestion from code review - gatsby serve tip

Co-Authored-By: Marcy Sutton <[email protected]>

* add partial porting note to introduction and hosting section

* consistent flag --