DOC: Advocate for using action from tagged release commit shas (#13)

* DOC: Advocate for using action from tagged release commit SHAs

* For security best practices, advocate that users of the action use it
  from known commit SHAs that correspond to tagged releases.
* Advocate that users use a Dependabot config file to update the action
  on new tags. This will bump the commit SHA and also bump the release
  tag in the comment of the commit SHA.
   - c.f. https://learn.scientific-python.org/development/guides/gha_basic/#updating

* DOC: Fix typo

* 'Intregration' -> 'Integration'

* Tighten up README

---------

Co-authored-by: Stefan van der Walt <[email protected]>

README.md

@@ -1,32 +1,53 @@
 # Nightly upload
 
-This provides a standard GitHub Action to upload nightly builds to the
-scientific-python nightly channel.
+This is a GitHub Action that uploads nightly builds to the [scientific-python nightly channel][],
+as recommended in [SPEC4 — Using and Creating Nightly Wheels][].
 
-In your Continuous Intregration pipeline once you've built you wheel, you can
-use the following snippet to upload to our central nightly repository:
+In a GitHub Actions workflow (`.github/workflows/*.yaml`), use the
+following snippet to upload built wheels to the repository:
 
 ```yml
 jobs:
   steps:
     ...
     - name: Upload wheel
-      uses: scientific-python/upload-nightly-action@main
+      uses: scientific-python/upload-nightly-action@8f0394fd2aa0c85d7364a9958652e8994e06b23c # 0.1.0
       with:
         artifacts_path: dist
         anaconda_nightly_upload_token: ${{secrets.UPLOAD_TOKEN}}
 ```
 
-To request access to the repository please open an issue on [this action
+Note that we recommend pinning the action against a specific SHA
+(rather than a tag), to guard against the unlikely event of upstream
+being compromised.
+
+# Updating the action
+
+You can [use Dependabot to keep the GitHub Action up to date][],
+with a `.github/dependabot.yml` config file similar to:
+
+```yaml
+version: 2
+updates:
+  # Maintain dependencies for GitHub Actions
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+```
+
+# Access
+
+To request access to the repository, please open an issue on [this action's
 repository](https://github.com/scientific-python/upload-nightly-action). You can
 then generate a token at `https://anaconda.org/scientific-python-nightly-wheels/settings/access`
-with _Allow write access to the API site_ and _Allow uploads to Standard Python repositories_
-permissions and add the token as a secret to your GitHub repository.
+with permissions to _Allow write access to the API site_ and _Allow uploads to Standard Python repositories_,
+and add the token as a secret to your GitHub repository.
 
 # Using nightly builds in CI
 
-To test those nightly build, you can use the following command to install from
-the nightly package.
+To test against nightly builds, you can use the following command to install from
+the nightly repository:
 
 ```sh
 python -m pip install \
@@ -37,29 +58,23 @@ python -m pip install \
   matplotlib
 ```
 
-Note that `--index-url` takes priority over `--extra-index-url`.
-Packages, and dependencies, with versions available on the
-[nightly package index][] will be installed from there before falling back to
-the [Python Package Index][PyPI] to install all remaining requested packages.
-
-```
-if package in nightly:
-   try to install from nightly
-else:
-   try to install from pypi
-```
+Note that `--index-url` takes priority over `--extra-index-url`, so
+that packages, and their dependencies, with versions available in the
+nightly channel will be installed before falling back to the [Python
+Package Index][PyPI].
 
-If you want to install nightly builds within your conda environment, you can specify an
-extra index in your YML file.
+To install nightly builds within a conda environment, specify an extra
+index in your `environment.yml`:
 
 ```yml
 name: test
 dependencies:
-  - pip
   - pip:
     - --pre --index-url https://pypi.anaconda.org/scientific-python-nightly-wheels/simple --extra-index-url https://pypi.org/simple
     - matplotlib
 ```
 
-[nightly package index]: https://anaconda.org/scientific-python-nightly-wheels
+[use Dependabot to keep the GitHub Action up to date]: https://learn.scientific-python.org/development/guides/gha_basic/#updating
 [PyPI]: https://pypi.org/
+[scientific-python nightly channel]: https://anaconda.org/scientific-python-nightly-wheels
+[SPEC4 — Using and Creating Nightly Wheels]: https://scientific-python.org/specs/spec-0004/