Update 0.5 release notes

docs/docs/the-marten-project/release-notes/0.5.md

@@ -88,6 +88,7 @@ article.category # => Category::BLOG
 * A new [`capture`](../../templates/reference/tags.md#capture) template tag was introduced to make it possible to easily assign the output of a block of code to a new variable.
 * The output of the [`csrf_token`](../../templates/reference/tags.md#csrf_token) template tag can now be outputted to a variable by leveraging the `as` keyword.
 * The `loop` variable, which is available when using the [`for`](../../templates/reference/tags.md#for) template tag, now supports `even?` and `odd?` attributes.
+* A new [`csrf_input`](../../templates/reference/tags.md#csrf_input) template tag was introduced to make it easier to insert the CSRF token into HTML forms. This new tag allows the generation of a hidden form input containing the CSRF token computed for the current request.
 
 #### Development