chore: import upstream snapshot with attribution

.github/pull_request_template.md

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+# Code Pull Requests
+
+Please provide the following:
+
+- a clear explanation of what your code does
+- if applicable, a reference to an issue
+- a reproducible test for your PR (code, config and data sample)
+
+# Documentation Pull Requests
+
+Note that the documentation HTML files are in `docs/` while the Markdown sources are in `mkdocs/docs`.
+
+If you are proposing a modification to the documentation you should change only the Markdown files.
+
+`api.md` is automatically generated from the docstrings in the code, so if you want to change something in that file, first modify `ludwig/api.py` docstring, then run `mkdocs/code_docs_autogen.py`, which will create `mkdocs/docs/api.md` .