Add version information for Str.Version

Author: stoned

doc/Type/Str.pod6

@@ -1144,6 +1144,8 @@ signature|/type/Signature#Coercion_type>, as for example:
     sub f(Version(Str) $want-version) { say $want-version.^name };
     f "1.2.3";  # OUTPUT: «Version␤»
 
+B<Note>: Available since version 6.e (2020.01 and later).
+
 =end pod
 
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