Restore version-added in string

jderusse · jderusse · commit 275b6e97ba7e · 2020-12-23T11:48:29.000+01:00
diff --git a/components/string.rst b/components/string.rst
@@ -8,6 +8,10 @@ The String Component
     The String component provides a single object-oriented API to work with
     three "unit systems" of strings: bytes, code points and grapheme clusters.
 
+.. versionadded:: 5.0
+
+    The String component was introduced in Symfony 5.0.
+
 Installation
 ------------
 
