minor #18422 [Validator] Give more details to the Password Strength (javiereguiluz)

This PR was merged into the 6.3 branch.

Discussion
----------

[Validator] Give more details to the Password Strength

Fixes #18412.

Commits
-------

3736d24 [Validator] Give more details to the Password Strength

Author: OskarStark

reference/constraints/PasswordStrength.rst

@@ -6,7 +6,10 @@ PasswordStrength
     The ``PasswordStrength`` constraint was introduced in Symfony 6.3.
 
 Validates that the given password has reached the minimum strength required by
-the constraint.
+the constraint. The strengh of the password is not evaluated with a set of
+predefined rules (include a number, use lowercase and uppercase characters,
+etc.) but by measuring the entropy of the password based on its length and the
+number of unique characters used.
 
 ==========  ===================================================================
 Applies to  :ref:`property or method <validation-property-target>`