chore: tweak manifest to match shift to markdown

{{cookiecutter.repo_name}}/MANIFEST.in

@@ -1,4 +1,4 @@
-include *.txt *.ini *.cfg *.rst *.toml
+include *.txt *.ini *.cfg *.md *.toml
 recursive-include {{ cookiecutter.repo_name }} *.ico *.png *.css *.gif *.jpg *.pt *.txt *.mak *.mako *.js *.html *.xml *.jinja2
 recursive-include tests *
 recursive-exclude * __pycache__