add md linter

Author: flexbox

.github/workflows/readme-checker.yml

@@ -0,0 +1,12 @@
+on: [pull_request]
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v3
+    - uses: DavidAnson/markdownlint-cli2-action@v11
+      with:
+        globs: |
+          *.md
+          !test/*.md

challenges/ecosystem/02.md

@@ -71,6 +71,8 @@ yarn add -D prettier eslint-config-prettier eslint-plugin-prettier
 - [ ] Update your `eslintrc.js` file to add the following rules:
 
 ```javascript
+// .eslintrc.js
+
 module.exports = {
   extends: ["expo", "prettier"],
   plugins: ["prettier"],
@@ -85,8 +87,11 @@ module.exports = {
 - [ ] Update your scripts on `package.json` to check errors.
 
 ```json
+<<<<<<< Updated upstream
 // package.json
 
+=======
+>>>>>>> Stashed changes
   "scripts": {
     ...
     "lint": "eslint --ignore-path .gitignore --ext .js,.ts,.tsx .",
@@ -244,8 +249,28 @@ yarn add -D eslint-plugin-simple-import-sort
           ["^\\./(?=.*/)(?!/?$)", "^\\.(?!/?$)", "^\\./?$"],
         ]
       }
+<<<<<<< Updated upstream
     ],
   },
+=======
+    ]
+  }
+};
+```
+
+- Create a `.prettierrc` file at the root of your project with the following content:
+
+```json
+// .prettierrc
+
+{
+  "$schema": "http://json.schemastore.org/prettierrc",
+  "semi": true,
+  "singleAttributePerLine": true,
+  "trailingComma": "none",
+  "tabWidth": 2, 
+  "singleQuote": false
+>>>>>>> Stashed changes
 }
 ```