Add CI workflow to do Arduino project-specific linting

On every push, pull request, and periodically, run Arduino Lint to check for common problems not related to the project
code.

The URLs in the workflow status badge are configured for the final location of the library, so they are expected to be broken while it is in the temporary development location.

Author: per1234

.github/workflows/check-arduino.yml

@@ -0,0 +1,28 @@
+name: Check Arduino
+
+# See: https://docs.github.com/en/actions/reference/events-that-trigger-workflows
+on:
+  push:
+  pull_request:
+  schedule:
+    # Run every Tuesday at 8 AM UTC to catch breakage caused by new rules added to Arduino Lint.
+    - cron: "0 8 * * TUE"
+  workflow_dispatch:
+  repository_dispatch:
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v2
+
+      - name: Arduino Lint
+        uses: arduino/arduino-lint-action@v1
+        with:
+          compliance: strict
+          # Change this to "update" once the library is added to the index.
+          library-manager: submit
+          # Always use this setting for official repositories. Remove for 3rd party projects.
+          official: true

README.md

@@ -1,5 +1,6 @@
 # `Arduino_Threads` library for Arduino
 
 [![Compile Examples status](https://github.com/arduino-libraries/Arduino_Threads/actions/workflows/compile-examples.yml/badge.svg)](https://github.com/arduino-libraries/Arduino_Threads/actions/workflows/compile-examples.yml)
+[![Check Arduino status](https://github.com/arduino-libraries/Arduino_Threads/actions/workflows/check-arduino.yml/badge.svg)](https://github.com/arduino-libraries/Arduino_Threads/actions/workflows/check-arduino.yml)
 
 This library makes it easy to use the multi-threading capability of [Arduino](https://www.arduino.cc/) boards that use an [Mbed OS](https://os.mbed.com/docs/mbed-os/latest/introduction/index.html)-based core library.