Install markdownlint VSCode extension, CLI and github config

cf https://github.com/github/markdownlint-github

Author: sampart

.markdownlint-cli2.cjs

@@ -0,0 +1,8 @@
+const options = require('@github/markdownlint-github').init()
+module.exports = {
+    config: options,
+    customRules: ["@github/markdownlint-github"],
+    outputFormatters: [
+      [ "markdownlint-cli2-formatter-pretty", { "appendLink": true } ] // ensures the error message includes a link to the rule documentation
+    ]
+}

.vscode/extensions.json

@@ -4,6 +4,7 @@
   // List of extensions which should be recommended for users of this workspace.
   "recommendations": [
     "amodio.tsl-problem-matcher",
+    "DavidAnson.vscode-markdownlint",
     "dbaeumer.vscode-eslint",
     "esbenp.prettier-vscode",
     "firsttris.vscode-jest-runner",