gh-37434: Document building from the monorepo using `PIP_CONSTRAINT=$SAGE_ROOT/constraints_pkgs.txt`
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This is aimed at the intermediate level, for users who wish to build a
set of distribution packages as supplied in `pkgs/` but without using
the wheelhouse infrastructure of Sage-the-distribution.
Documentation included in the files.
It can also be tested using new tox environments defined in
`pkgs/sagemath-standard/tox.ini`, and is tested on GH Actions:
https://github.com/mkoeppe/sage/actions/workflows/ci-linux-
incremental.yml?query=branch%3Aconstraints_pkgs
- this also provides the missing automatic test for the **sagemath-
standard** distribution built out of `pkgs/sagemath-standard/`
Marked as critical because it is hoped to ease the adoption of
modularized distribution packages by downstream packagers.
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- Depends on #38515 (merged here)
- Depends on #38500 (merged here)
URL: https://github.com/sagemath/sage/pull/37434
Reported by: Matthias Köppe
Reviewer(s): François Bissey, Kwankyu Lee, Matthias Köppe
