Clean up sdist and build instructions

[rly]

The build instructions in pyproject.toml were confusing. In addition, the sdist did not include all the files that document the package, such as the changelog and requirements files.

Before:

❯ tar -xzvf ndx_pose-0.2.0.tar.gz 
x ndx_pose-0.2.0/docs/Makefile
x ndx_pose-0.2.0/docs/README.md
x ndx_pose-0.2.0/docs/make.bat
x ndx_pose-0.2.0/docs/source/conf.py
x ndx_pose-0.2.0/docs/source/conf_doc_autogen.py
x ndx_pose-0.2.0/docs/source/credits.rst
x ndx_pose-0.2.0/docs/source/description.rst
x ndx_pose-0.2.0/docs/source/format.rst
x ndx_pose-0.2.0/docs/source/index.rst
x ndx_pose-0.2.0/docs/source/release_notes.rst
x ndx_pose-0.2.0/docs/source/_static/theme_overrides.css
x ndx_pose-0.2.0/spec/ndx-pose.extensions.yaml
x ndx_pose-0.2.0/spec/ndx-pose.namespace.yaml
x ndx_pose-0.2.0/src/pynwb/README.md
x ndx_pose-0.2.0/src/pynwb/ndx_pose/__init__.py
x ndx_pose-0.2.0/src/pynwb/ndx_pose/pose.py
x ndx_pose-0.2.0/src/pynwb/ndx_pose/io/__init__.py
x ndx_pose-0.2.0/src/pynwb/ndx_pose/io/pose.py
x ndx_pose-0.2.0/src/pynwb/ndx_pose/testing/mock/__init__.py
x ndx_pose-0.2.0/src/pynwb/ndx_pose/testing/mock/pose.py
x ndx_pose-0.2.0/src/pynwb/tests/__init__.py
x ndx_pose-0.2.0/src/pynwb/tests/test_example_usage.py
x ndx_pose-0.2.0/src/pynwb/tests/back_compat/generate_data_0.1.1.py
x ndx_pose-0.2.0/src/pynwb/tests/back_compat/test_read.py
x ndx_pose-0.2.0/src/pynwb/tests/integration/hdf5/__init__.py
x ndx_pose-0.2.0/src/pynwb/tests/integration/hdf5/test_pose.py
x ndx_pose-0.2.0/src/pynwb/tests/unit/__init__.py
x ndx_pose-0.2.0/src/pynwb/tests/unit/test_pose.py
x ndx_pose-0.2.0/.gitignore
x ndx_pose-0.2.0/LICENSE.txt
x ndx_pose-0.2.0/README.md
x ndx_pose-0.2.0/pyproject.toml
x ndx_pose-0.2.0/PKG-INFO

After:

❯ tar -xzvf ndx_pose-0.2.0.tar.gz 
x ndx_pose-0.2.0/CHANGELOG.md
x ndx_pose-0.2.0/requirements-dev.txt
x ndx_pose-0.2.0/requirements-min.txt
x ndx_pose-0.2.0/docs/Makefile
x ndx_pose-0.2.0/docs/README.md
x ndx_pose-0.2.0/docs/make.bat
x ndx_pose-0.2.0/docs/source/conf.py
x ndx_pose-0.2.0/docs/source/conf_doc_autogen.py
x ndx_pose-0.2.0/docs/source/credits.rst
x ndx_pose-0.2.0/docs/source/description.rst
x ndx_pose-0.2.0/docs/source/format.rst
x ndx_pose-0.2.0/docs/source/index.rst
x ndx_pose-0.2.0/docs/source/release_notes.rst
x ndx_pose-0.2.0/docs/source/_static/theme_overrides.css
x ndx_pose-0.2.0/spec/ndx-pose.extensions.yaml
x ndx_pose-0.2.0/spec/ndx-pose.namespace.yaml
x ndx_pose-0.2.0/src/matnwb/README.md
x ndx_pose-0.2.0/src/pynwb/README.md
x ndx_pose-0.2.0/src/pynwb/ndx_pose/__init__.py
x ndx_pose-0.2.0/src/pynwb/ndx_pose/pose.py
x ndx_pose-0.2.0/src/pynwb/ndx_pose/io/__init__.py
x ndx_pose-0.2.0/src/pynwb/ndx_pose/io/pose.py
x ndx_pose-0.2.0/src/pynwb/ndx_pose/testing/mock/__init__.py
x ndx_pose-0.2.0/src/pynwb/ndx_pose/testing/mock/pose.py
x ndx_pose-0.2.0/src/pynwb/tests/__init__.py
x ndx_pose-0.2.0/src/pynwb/tests/test_example_usage.py
x ndx_pose-0.2.0/src/pynwb/tests/back_compat/generate_data_0.1.1.py
x ndx_pose-0.2.0/src/pynwb/tests/back_compat/test_read.py
x ndx_pose-0.2.0/src/pynwb/tests/integration/hdf5/__init__.py
x ndx_pose-0.2.0/src/pynwb/tests/integration/hdf5/test_pose.py
x ndx_pose-0.2.0/src/pynwb/tests/unit/__init__.py
x ndx_pose-0.2.0/src/pynwb/tests/unit/test_pose.py
x ndx_pose-0.2.0/src/spec/create_extension_spec.py
x ndx_pose-0.2.0/.gitignore
x ndx_pose-0.2.0/LICENSE.txt
x ndx_pose-0.2.0/README.md
x ndx_pose-0.2.0/pyproject.toml
x ndx_pose-0.2.0/PKG-INFO

This PR cleans up pyproject.toml to include those the missing files, remove the global build configuration which is not recommended by hatch, and adds some comments.

Thanks @h-mayorquin