Add pre-commit configuration and integration for REUSE.software.

pre-commit.com provides a way to configure pre-commit hooks for multiple
tools, including `reuse lint` (configured here), isort, black, and more.

This is also integrated with GitHub actions in the example configuration.

.github/workflows/build.yml

@@ -42,11 +42,15 @@ jobs:
       # (e.g. - apt-get: gettext, etc; pip: circuitpython-build-tools, requirements.txt; etc.)
       run: |
         source actions-ci/install.sh
-    - name: Pip install pylint, black, & Sphinx
+    - name: Pip install pylint, black, Sphinx, pre-commit
       run: |
-        pip install --force-reinstall pylint black==19.10b0 Sphinx sphinx-rtd-theme
+        pip install --force-reinstall pylint black==19.10b0 Sphinx sphinx-rtd-theme pre-commit
     - name: Library version
       run: git describe --dirty --always --tags
+    - name: Pre-commit hooks
+      run: |
+        pre-commit install
+        pre-commit run --all-files
     - name: Check formatting
       run: |
         black --check --target-version=py35 .

.pre-commit-config.yaml

@@ -0,0 +1,9 @@
+# SPDX-FileCopyrightText: 2020 Diego Elio Pettenò
+#
+# SPDX-License-Identifier: Unlicense
+
+repos:
+-   repo: https://github.com/fsfe/reuse-tool
+    rev: latest
+    hooks:
+    - id: reuse