Fix caption grammar in _InitCommand.rst.txt

It is the second case which needs the apostrophe.

Author: franzholz

Documentation/_Includes/_InitCommand.rst.txt

@@ -1,4 +1,4 @@
 ..  code-block:: bash
-    :caption: Execute in extension root, the directory that contains your extensions composer.json
+    :caption: Execute in extension root, the directory that contains your extension's composer.json
 
     docker run --rm --pull always -v $(pwd):/project -it ghcr.io/typo3-documentation/render-guides:latest init