The internals documentation is scattered in markdown files in the codebase, as well as parts which are in the dev guide.  We would like to have it in one place, versioned along with the code (unlike the dev guide). 



<!-- gh-linked-prs -->
### Linked PRs
* gh-119787
* gh-119815
* gh-120077
* gh-120137
* gh-120134
* gh-120445
* gh-121009
* gh-121601
<!-- /gh-linked-prs -->

create an internals documentation folder in the cpython repo
This is a GitHub Issue
repo:cpython
owner:python
Title : create an internals documentation folder in the cpython repo
Issue date:

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The internals documentation is scattered in markdown files in the codebase, as well as parts which are in the dev guide.  We would like to have it in one place, versioned along with the code (unlike the dev guide). 



<!-- gh-linked-prs -->
### Linked PRs
* gh-119787
* gh-119815
* gh-120077
* gh-120137
* gh-120134
* gh-120445
* gh-121009
* gh-121601
<!-- /gh-linked-prs -->

--- end body ---
