Add precisions to documentation (#16)

Co-authored-by: Bertrand Paquet <[email protected]>

Author: antoineverin

website/docs/index.html.markdown

@@ -8,7 +8,13 @@ description: |-
 
 # ElkAliases Provider
 
-The ElkAliases provider gives the ability to deploy index template to a ElasticSearch server
+The ElkAliases provider gives the ability to add aliases on indexes, created by an [index templates](https://registry.terraform.io/providers/elastic/elasticstack/latest/docs/resources/elasticsearch_index_template).
+
+With the current provider from elasticstack, there is no solution to [add aliases to an existing index](https://github.com/elastic/terraform-provider-elasticstack/issues/285).
+To solve this problem, we have created this provider, which enables you through the `elkaliases_index_aliases` resource to add aliases to existing index or data stream.
+If you use this provider, you should not declare `alias` with `elasticstack_elasticsearch_index_template` resource.
+
+This provider is a workaround, waiting for a long term solution in [the official provider](https://registry.terraform.io/providers/elastic/elasticstack/latest).
 
 Use the navigation to the left to read about the available resources.
 

website/docs/r/elkaliases_index_aliases.markdown

@@ -8,7 +8,10 @@ description: |-
 
 # alkaliases\_index
 
-The ``elkaliases_index_aliases`` resource creates aliases in an index
+The ``elkaliases_index_aliases`` resource creates aliases in an existing index.
+
+
+~> **Note**: The index needs to already exist at deployment time. This means that you cannot create an index template and apply aliases to it directly. You need to create an index or data stream first.
 
 ## Usage