minor symfony#50841 Readme: Replace Stack Overflow with GitHub Discussions (lyrixx)

This PR was merged into the 5.4 branch.

Discussion
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Readme: Replace Stack Overflow with GitHub Discussions

| Q             | A
| ------------- | ---
| Branch?       | 5.4
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Tickets       |
| License       | MIT
| Doc PR        |

The link leads to https://symfony.com/community
And there we don't talk about SO, but only GH Discussions

Commits
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b1dc7c8 Readme: Replace Stack Overflow with GitHub Discussions

Author: wouterj

README.md

@@ -38,7 +38,7 @@ Community
 ---------
 
 * [Join the Symfony Community][11] and meet other members at the [Symfony events][12].
-* [Get Symfony support][13] on Stack Overflow, Slack, IRC, etc.
+* [Get Symfony support][13] on GitHub Discussions, Slack, etc.
 * Follow us on [GitHub][14], [Twitter][15] and [Facebook][16].
 * Read our [Code of Conduct][24] and meet the [CARE Team][25].