Add GitHub Action for checking links in Markdown content.

.github/workflows/spell-check.yml

@@ -1,18 +0,0 @@
-name: SpellCheck
-
-on:
-  pull_request:
-  push:
-  schedule:
-  - cron: '30 12 * * *'
-  workflow_dispatch:
-
-jobs:
-  spellcheck:
-    runs-on: ubuntu-latest
-    steps:
-    - uses: actions/checkout@v3
-    - uses: tbroadley/spellchecker-cli-action@v1.1.1
-      with:
-        dictionaries: '.github/dictionary.txt'
-        files: '*.md doc/*.md helpers/*.md'