Update the postinstall to reflect the non-existing admin

POSTINSTALL.md

@@ -1,17 +1,11 @@
-This app instance is pre-setup with an admin account.
+This installation does not come with any pre-setup users. Create new users in the registration form of the app.
 
-The initial credentials are:
-
-`username: admin`
-
-`password: 123123`
-
-**Please change the admin password on first login**
+Taiga does not come with any global admin panel, every user creating a new project is the admin of that project.
 
 === sso ===
 
 This app integrates with Cloudron authentication. Cloudron users can login and use Taiga.
 
-However, _admin_ status of Cloudron users is not carried over to Taiga but is also not required for a working setup.
+Taiga does not come with any global admin panel, every user creating a new project is the admin of that project.
 
 The public registration is disabled, if required, please install an instance of Taiga without Cloudron user integration.