minor symfony#53265 [Notifier] [SmsSluzba] Add warning to README (OskarStark)

This PR was merged into the 7.1 branch.

Discussion
----------

[Notifier] [SmsSluzba] Add warning to README

| Q             | A
| ------------- | ---
| Branch?       | 7.1
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Issues        | --
| License       | MIT

Displays like:

> [!CAUTION]
> This bridge uses query parameters to provide credentials to the sms-sluzba.cz API!

Commits
-------

179dcf1 [Notifier][SmsSluzba] Add warning to README

Author: fabpot

src/Symfony/Component/Notifier/Bridge/SmsSluzba/README.md

@@ -3,6 +3,9 @@ sms-sluzba.cz Notifier
 
 Provides [sms-sluzba.cz](https://www.sms-sluzba.cz/) integration for Symfony Notifier.
 
+> [!CAUTION]
+> This bridge uses query parameters to provide credentials to the sms-sluzba.cz API!
+
 DSN example
 -----------