minor symfony#30538 [Messenger] Fix README about BC promise (nicolas-…

…grekas)

This PR was merged into the 4.2 branch.

Discussion
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[Messenger] Fix README about BC promise

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

We don't have a BC *break* policy :)
Should be applied to MIME and HttpClient when merging into master.

Commits
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9b2af69 Fix README about BC promise

src/Symfony/Component/Messenger/README.md

@@ -4,9 +4,10 @@ Messenger Component
 The Messenger component helps application send and receive messages to/from other applications or via
 message queues.
 
-**This Component is experimental**. [Experimental
-features](https://symfony.com/doc/current/contributing/code/experimental.html)
-are not covered by Symfony's BC-break policy.
+**This Component is experimental**.
+[Experimental features](https://symfony.com/doc/current/contributing/code/experimental.html)
+are not covered by Symfony's
+[Backward Compatibility Promise](https://symfony.com/doc/current/contributing/code/bc.html).
 
 Resources
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