Fix displaced retype markup in how-to (closes #693)

docs/how-to.md

@@ -555,6 +555,7 @@ def index # controller action
   @pagy_nebulae, @nebulae = pagy(Nebula.all, page_param: :page_nebulae)
 end
 ```
+===
 
 ## Wrap existing pagination with pagy_calendar
 
@@ -580,8 +581,6 @@ to different existing statements.
 
 Then follow the [calendar extra documentation](extras/calendar.md) for more details.
 
-===
-
 ## Paginate only max_pages, regardless the count
 
 In order to limit the pagination to a maximum number of pages, you can pass the `:max_pages` variable.