Uses RST substitution to put badges in 1 line.

It might be some update to the Github's RST renderer caused badges display in multi lines. use RST substitution to put badges in 1 line.

README.rst

@@ -1,15 +1,17 @@
-.. image:: https://img.shields.io/pypi/v/twine.svg
+.. |twine-version| image:: https://img.shields.io/pypi/v/twine.svg
    :target: https://pypi.org/project/twine
 
-.. image:: https://img.shields.io/pypi/pyversions/twine.svg
+.. |python-versions| image:: https://img.shields.io/pypi/pyversions/twine.svg
    :target: https://pypi.org/project/twine
 
-.. image:: https://img.shields.io/readthedocs/twine
+.. |docs-badge| image:: https://img.shields.io/readthedocs/twine
    :target: https://twine.readthedocs.io
 
-.. image:: https://img.shields.io/github/actions/workflow/status/pypa/twine/main.yml?branch=main
+.. |build-badge| image:: https://img.shields.io/github/actions/workflow/status/pypa/twine/main.yml?branch=main
    :target: https://github.com/pypa/twine/actions
 
+|twine-version| |python-versions| |docs-badge| |build-badge|
+
 twine
 =====