Doc: use correct package names for turndown (#9882)

Co-authored-by: Laurent Cozic <laurent22@users.noreply.github.com>

.github/PULL_REQUEST_TEMPLATE

@@ -20,6 +20,6 @@ If it's not related to any platform (such as a translation, change to the docume
 
 Then please append the issue that you've addressed or fixed. Use "Resolves #123" for new features or improvements and "Fixes #123" for bug fixes.
 
-AND PLEASE READ THE GUIDE: https://github.com/laurent22/joplin/blob/dev/CONTRIBUTING.md
+AND PLEASE READ THE GUIDE: https://github.com/laurent22/joplin/blob/dev/readme/dev/index.md
 
--->
+-->

packages/turndown-plugin-gfm/README.md

@@ -17,7 +17,7 @@ This is a fork of the original [turndown-plugin-gfm](https://github.com/domchris
 npm:
 
 ```
-npm install joplin-turndown-plugin-gfm
+npm install @joplin/turndown-plugin-gfm
 ```
 
 ## Usage

packages/turndown/README.md

@@ -30,7 +30,7 @@ The `src/` folder of this fork is currently based on commit `97e4535ca76bb2e70d9
 npm:
 
 ```
-npm install joplin-turndown
+npm install @joplin/turndown
 ```
 
 Browser:

packages/turndown/package.json

@@ -36,7 +36,8 @@
   "license": "MIT",
   "repository": {
     "type": "git",
-    "url": "https://github.com/laurent22/joplin-turndown.git"
+    "url": "https://github.com/laurent22/joplin.git",
+    "directory": "packages/turndown"
   },
   "scripts": {
     "build-all": "npm run build-cjs && npm run build-es && npm run build-umd && npm run build-iife",