added filter deprecation message in the docs

Author: saimaz

docs/Filter/index.md

@@ -1,5 +1,7 @@
 # Filter
 
+> WARNING: Filters are deprecated since 1.1 and will be removed in 2.0. Elasticsearch from 2.0 casts queries the same way as filters, so there is no reason to have both. More information in [the elasticsearch docs](https://www.elastic.co/guide/en/elasticsearch/reference/2.0/query-dsl-filters.html)
+
 Objective filter builder represents all available [Elasticsearch filters][1].
 
 To form a filtered query you have to create `Search` object. See below an example of match all filter usage.

docs/index.md

@@ -9,6 +9,8 @@ Everything starts from the `Search` object. We recommend first to take a look at
 - [Build Filters](Filter/index.md)
 - [Build Aggregations](Aggregation/index.md)
 
+> WARNING: Filters are deprecated since 1.1 and will be removed in 2.0. Elasticsearch from 2.0 casts queries the same way as filters, so there is no reason to have both. More information in [the elasticsearch docs](https://www.elastic.co/guide/en/elasticsearch/reference/2.0/query-dsl-filters.html)
+
 ### How to
 - [How to Search](HowTo/HowToSearch.md)
 - [How to set custom parameters to Search](HowTo/CustomParameters.md)