src/doc/en/developer/packaging_sage_library.rst: Add bootstrap to tes…

…ting instructions to avoid the trap of #32868

src/doc/en/developer/packaging_sage_library.rst

@@ -445,7 +445,7 @@ Following the comments in the file
 ``SAGE_ROOT/pkgs/sagemath-standard/tox.ini``, we can try the following
 command::
 
-  $ ./sage -sh -c '(cd pkgs/sagemath-standard && SAGE_NUM_THREADS=16 tox -v -v -v -e py39-sagewheels-nopypi)'
+  $ ./bootstrap && ./sage -sh -c '(cd pkgs/sagemath-standard && SAGE_NUM_THREADS=16 tox -v -v -v -e py39-sagewheels-nopypi)'
 
 This command does not make any changes to the normal installation of
 Sage. The virtual environment is created in a subdirectory of
@@ -470,14 +470,14 @@ without depending on optional packages, but without the packages
 
 Again we can run the test with ``tox`` in a separate virtual environment::
 
-  $ ./sage -sh -c '(cd pkgs/sagemath-standard-no-symbolics && SAGE_NUM_THREADS=16 tox -v -v -v -e py39-sagewheels-nopypi)'
+  $ ./bootstrap && ./sage -sh -c '(cd pkgs/sagemath-standard-no-symbolics && SAGE_NUM_THREADS=16 tox -v -v -v -e py39-sagewheels-nopypi)'
 
 Some small distributions, for example the ones providing the two
 lowest levels, **sagemath-objects** and **sagemath-categories**
 (https://trac.sagemath.org/ticket/29865), can be installed and tested
 without relying on the wheels from the Sage build::
 
-  $ ./sage -sh -c '(cd pkgs/sagemath-objects && SAGE_NUM_THREADS=16 tox -v -v -v -e py39)'
+  $ ./bootstrap && ./sage -sh -c '(cd pkgs/sagemath-objects && SAGE_NUM_THREADS=16 tox -v -v -v -e py39)'
 
 This command finds the declared build-time and run-time dependencies
 on PyPI, either as source tarballs or as prebuilt wheels, and builds