Add .gitignore, .editorconfig, CONTRIBUTING.md (#43)

See https://github.com/python/typing/commits/master/CONTRIBUTING.md for a full history of that file.

.editorconfig

@@ -0,0 +1,12 @@
+root = true
+
+[*.{py,pyi,rst,md,yml,yaml,toml,json}]
+trim_trailing_whitespace = true
+insert_final_newline = true
+indent_style = space
+
+[*.{py,pyi,toml,json}]
+indent_size = 4
+
+[*.{yml,yaml}]
+indent_size = 2

.gitignore

@@ -0,0 +1,17 @@
+MANIFEST
+
+__pycache__/
+build/
+dist/
+tmp/
+venv*/
+
+.cache/
+.idea/
+.tox/
+.venv*/
+.vscode/
+
+*.swp
+*.pyc
+*.egg-info/

CONTRIBUTING.md

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+Code in this repository should follow CPython's style guidelines and
+contributors need to sign the PSF Contributor Agreement.
+
+# typing\_extensions
+
+The `typing_extensions` module provides a way to access new features from the standard
+library `typing` module in older versions of Python. For example, Python 3.10 adds
+`typing.TypeGuard`, but users of older versions of Python can use `typing_extensions` to
+use `TypeGuard` in their code even if they are unable to upgrade to Python 3.10.
+
+If you contribute the runtime implementation of a new `typing` feature to CPython, you
+are encouraged to also implement the feature in `typing_extensions`. Because the runtime
+implementation of much of the infrastructure in the `typing` module has changed over
+time, this may require different code for some older Python versions.
+
+`typing_extensions` may also include experimental features that are not yet part of the
+standard library, so that users can experiment with them before they are added to the
+standard library. Such features should ideally already be specified in a PEP or draft
+PEP.
+
+`typing_extensions` supports Python versions 3.7 and up.
+
+# Versioning scheme
+
+Starting with version 4.0.0, `typing_extensions` uses
+[Semantic Versioning](https://semver.org/). The major version is incremented for all
+backwards-incompatible changes.
+
+# Workflow for PyPI releases
+
+- Ensure that GitHub Actions reports no errors.
+
+- Update the version number in `typing_extensions/pyproject.toml` and in
+  `typing_extensions/CHANGELOG.md`.
+
+- Make sure your environment is up to date
+
+ - `git checkout master`
+ - `git pull`
+ - `python -m pip install --upgrade build twine`
+
+- Build the source and wheel distributions:
+
+  - `cd typing_extensions`
+  - `rm -rf dist/`
+  - `python -m build .`
+
+- Install the built distributions locally and test (if you were using `tox`, you already
+  tested the source distribution).
+
+- Run `twine upload dist/*`.
+
+- Tag the release. The tag should be just the version number, e.g. `4.1.1`.
+
+- `git push --tags`