Create migration guide from alpha.8 to alpha.9

Co-authored-by: soupette

docs/3.x.x/en/SUMMARY.md

@@ -54,3 +54,4 @@
 ### Migration
 * [Migrating from v1 to v3](migration/migration-guide.md)
 * [Migrating from 3.0.0-alpha.7.4 to 3.0.0-alpha.8](migration/migration-guide-alpha-7-4-to-alpha-8.md)
+* [Migrating from 3.0.0-alpha.8 to 3.0.0-alpha.9](migration/migration-guide-alpha-8-to-alpha-9.md)

docs/3.x.x/en/migration/migration-guide-alpha-8-to-alpha-9.md

@@ -0,0 +1,71 @@
+# Migrating from 3.0.0-alpha.8 to 3.0.0-alpha.9
+
+**Here are the major changes:**
+
+- Put roles' permissions in database
+- Providers connection (Facebook, GitHub, ...)
+
+> Feel free to [join us on Slack](http://slack.strapi.io) and ask questions about the migration process.
+
+
+## Getting started
+
+Install Strapi `alpha.9` globally on your computer. To do so run `npm install strapi@3.0.0-alpha.9 -g`.
+
+When it's done, generate a new empty project `strapi new myNewProject` (don't pay attention to the database configuration).
+
+## Configurations
+
+You will have to update just 2 files: `package.json` and `request.json`
+
+- Edit the Strapi's dependencies version: (move Strapi's dependencies to `3.0.0-alpha.9` version) in `package.json` file
+
+```json
+{
+  "dependencies": {
+    "lodash": "4.x.x",
+    "strapi": "3.0.0-alpha.9",
+    "strapi-mongoose": "3.0.0-alpha.9"
+  }
+}
+```
+
+
+- Edit the `session.enabled` settings to `true` in each environment file: `/configs/environments/***/request.json`
+
+```json
+{
+  "session": {
+    "enabled": true
+  }
+}
+```
+
+
+## Update the Admin
+
+Delete your old admin folder and replace it by the new one.
+
+
+## Update the Plugins
+
+Copy this file `/plugins/users-permissions/config/jwt.json` **from your old project** and paste it in the corresponding one in your new project.
+
+Copy the fields and relations you had in your `/plugins/users-permissions/models/User.settings.json` file in the new one.
+
+Then, delete your old `plugins` folder and replace it by the new one.
+
+
+## ⚠️  Roles update
+
+Roles are now stored in your database. You will have to re-create and configure them via the admin dashboard.
+
+
+## ⚠️  User collection/table name has changed
+
+If you have an existing set of users in your database you will have to rename the collection/table from `user` to `users-permissions_user`.
+
+Then update all your users by changing the old role id by the new one which is in `users-permissions_role` collection/table.
+
+
+That's all, you have now upgraded to Strapi `alpha.9`.