Change Instagram env vars to Facebook for instagram provider gitroomhq/postiz-app#424

Author: jamesread

pages/providers/instagram.mdx

@@ -63,8 +63,8 @@ Go to advanced permission and request access for the following scopes:
 Go to basic permissions copy your App ID and App Secret and paste them in your `.env` file
 
 ```env
-INSTAGRAM_APP_ID="app id"
-INSTAGRAM_APP_SECRET="app secret"
+FACEBOOK_APP_ID="app id"
+FACEBOOK_APP_SECRET="app secret"
 ```
 
 Instagram should now be working!