[ReadMe] Add warning about data loss

README.md

@@ -8,10 +8,25 @@ That can easily lead to confidentiality breaches when multiple organizations sha
 This package tries to provide a solution to this problem, by linking each customer to a specific mailbox.
 The information related to a customer, especially their e-mail address, is only shown to users with access to the related mailbox.
 
+## Data loss warning
+
+When this module is installed, it will link customers to mailboxes.
+Customers added once this module is active will be linked to mailboxes too.
+On uninstallation, simply unlinking them could cause several problems:
+- It could break unicity constraints, as two customers linked to disctinct mailboxes are allowed to use the same e-mail address as long as the module is active;
+- It would break the confidentiality promise, by letting all users having access to all customers.
+
+To avoid these problems, on the module uninstallation all the customers linked to mailboxes are dropped from the database.
+This is an irreversible operation, the customers deleted that way are gone for good.
+
+So it is highly recommended to backup your customers database:
+- Before installing this module;
+- Before uninstalling this module.
+
 ## Disclaimer
 
 This is still a work in progress.
-Using any version prior to the (not yet released) 1.0.0 will lead to irrecuperable data loss.
+Using any version prior to the (not yet released) 1.0.0 might lead to irrecuperable data loss.
 You have been warned.
 
 ## Installation instructions