Add markdownlint to package json

Author: tidy-dev

.markdownlint.js

@@ -0,0 +1,2 @@
+const markdownlintGitHub = require('@github/markdownlint-github')
+module.exports = markdownlintGitHub.init()

package.json

@@ -25,6 +25,7 @@
     "compile:script": "tsc -P script/tsconfig.json",
     "lint": "yarn prettier && yarn lint:src",
     "lint:fix": "yarn prettier --write && yarn lint:src:fix",
+    "markdownlint": "markdownlint **/*.{md,mdx} --config .markdownlint.js --rules node_modules/@github/markdownlint-github --ignore node_modules --ignore gemoji",
     "prettier": "prettier --check \"./**/*.{ts,tsx,js,json,jsx,scss,html,yaml,yml}\"",
     "lint:src": "yarn eslint-check && yarn eslint",
     "lint:src:fix": "yarn eslint --fix",