minor #1277 [Docs] Add caution alert when bundle require StimulusBundle (ker0x)

This PR was merged into the 2.x branch.

Discussion
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[Docs] Add caution alert when bundle require StimulusBundle

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| Issues        | To complement  #1276
| License       | MIT

This PR add a `caution` alert at the beginning of `Installation` section for all bundle requiring StimulusBundle

Commits
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743d44a5 [Docs] Add caution alert when bundle require StimulusBundle

Author: weaverryan

doc/index.rst

@@ -72,9 +72,11 @@ Want some demos? Check out https://ux.symfony.com/live-component#demo
 Installation
 ------------
 
-Before you start, make sure you have `StimulusBundle configured in your app`_.
+.. caution::
+
+    Before you start, make sure you have `StimulusBundle configured in your app`_.
 
-Now install the library with:
+Install the bundle using Composer and Symfony Flex:
 
 .. code-block:: terminal