added version information in the doc

doc/02-Twig-for-Template-Designers.markdown

@@ -882,7 +882,7 @@ Within the translatable string, the special `count` variable always contain
 the count value (here the value of `apple_count`).
 
 Within an expression or in a tag, you can use the `trans` filter to translate
-simple strings or variables:
+simple strings or variables (new in Twig 0.9.9):
 
     [twig]
     {{ var|default(default_value|trans) }}

doc/06-Recipes.markdown

@@ -249,7 +249,8 @@ Complex Translations within an Expression or Tag
 
 Translations can be done with both the `trans` tag and the `trans` filter. The
 filter is less powerful as it only works for simple variables or strings. For
-more complex scenario, like pluralization, you can use a two-step strategy:
+more complex scenario, like pluralization, you can use a two-step strategy
+(new in Twig 0.9.9):
 
     [twig]
     {# assign the translation to a temporary variable #}