Move linters from CircleCI to GitHub actions (#289)

* Move linters from CircleCI to GitHub actions

* Update README with fresh black links and a GitHub actions badge

* Only trigger push workflow on master

* Remove CircleCI integration

Author: gahjelle

.circleci/config.yml

@@ -0,0 +1,57 @@
+# Check that code is formatted consistently
+#
+# Available Python versions:
+# https://raw.githubusercontent.com/actions/python-versions/main/versions-manifest.json
+
+name: linters
+on: 
+  push:
+    branches:
+      - master
+  pull_request:
+
+jobs:
+  tests:
+    name: ${{ matrix.name }}
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - {name: Linux311, python: '3.11.0-rc.1', os: ubuntu-latest}
+    steps:
+    - name: Check out repository
+      uses: actions/checkout@v2
+
+    - name: Set up Python 
+      uses: actions/setup-python@v2
+      with:
+        python-version: ${{ matrix.python }}
+
+    - name: Restore cache
+      id: cache
+      uses: actions/cache@v3
+      with:
+        path: ./venv
+        key: ${{ matrix.name }}-pip-${{ hashFiles('requirements.txt') }}
+        restore-keys: |
+          ${{ matrix.name }}-pip-
+
+    - name: Install dependencies
+      if: steps.cache.outputs.cache-hit != 'true'
+      run: |
+        python -m venv venv
+        . venv/bin/activate
+        python -m pip install --upgrade pip
+        python -m pip install -r requirements.txt
+
+    - name: Check code style
+      run: |
+        . venv/bin/activate
+        python -m flake8
+        python -m black --check .
+
+    - name: Check directory layout
+      run: |
+        . venv/bin/activate
+        python .github/workflows/dircheck.py

.circleci/dircheck.py .github/workflows/dircheck.py.circleci/dircheck.py renamed to .github/workflows/dircheck.py

@@ -2,19 +2,20 @@
 
 Bonus materials, exercises, and example projects for Real Python's [Python tutorials](https://realpython.com).
 
-Build Status: [![CircleCI](https://circleci.com/gh/realpython/materials.svg?style=svg)](https://circleci.com/gh/realpython/materials)
+Build Status:
+[![GitHub Actions](https://img.shields.io/github/workflow/status/realpython/materials/linters?label=build)](https://github.com/realpython/materials/actions)
 
 ## Got a Question?
 
-The best way to get support for Real Python courses & articles and code in this repository is to join one of our [weekly Office Hours calls](https://realpython.com/office-hours/) or to ask your question in the [RP Community Slack](https://realpython.com/community/). 
+The best way to get support for Real Python courses, articles, and code in this repository is to join one of our [weekly Office Hours calls](https://realpython.com/office-hours/) or to ask your question in the [RP Community Slack](https://realpython.com/community/).
 
-Due to time constraints we cannot provide 1:1 support via GitHub. See you on Slack or on the next Office Hours call 🙂
+Due to time constraints, we cannot provide 1:1 support via GitHub. See you on Slack or on the next Office Hours call 🙂
 
 ## Adding Source Code & Sample Projects to This Repo (RP Contributors)
 
 ### Running Code Style Checks
 
-We use [flake8](http://flake8.pycqa.org/en/latest/) and [black](https://github.com/ambv/black) to ensure a consistent code style for all of our sample code in this repository.
+We use [flake8](http://flake8.pycqa.org/en/latest/) and [black](https://black.readthedocs.io/) to ensure a consistent code style for all of our sample code in this repository.
 
 Run the following commands to validate your code against the linters:
 
@@ -25,11 +26,11 @@ $ black --check .
 
 ### Running Python Code Formatter
 
-We're using a tool called [black](https://github.com/ambv/black) on this repo to ensure consistent formatting. On CI it runs in "check" mode to ensure any new files added to the repo are following PEP 8. If you see linter warnings that say something like "would reformat some_file.py" it means black disagrees with your formatting. 
+We're using a tool called [black](https://black.readthedocs.io/) on this repo to ensure consistent formatting. On CI it runs in "check" mode to ensure any new files added to the repo follow PEP 8. If you see linter warnings that say something like "would reformat some_file.py" it means that black disagrees with your formatting.
 
-**The easiest way to resolve these errors is to just run Black locally on the code and then committing those changes, as explained below.**
+**The easiest way to resolve these errors is to run Black locally on the code and then commit those changes, as explained below.**
 
-To automatically re-format your code to be consistent with our code style guidelines, run [black](https://github.com/ambv/black) in the repository root folder:
+To automatically re-format your code to be consistent with our code style guidelines, run [black](https://black.readthedocs.io/) in the repository root folder:
 
 ```sh
 $ black .