Add mandatory requirements to docs

Author: tbauriedel

README.md

@@ -3,7 +3,7 @@
 ![Test ElasticStack](https://github.com/NETWAYS/ansible-collection-elasticstack/actions/workflows/test_full_stack.yml/badge.svg)
 
 > [!CAUTION]
-> This branch has some breaking changes. Be careful using it!
+> This branch has some breaking changes. Be careful using it! Everything after commit 3d6673f6d526afeb0fd7ba382d067d76bd10bbd6 is affected!
 
 This collection installs and manages the Elastic Stack. It provides roles for every component of the Stack. Furthermore, it is possible to differentiate between Enterprise or OSS releases.
 
@@ -13,6 +13,9 @@ Every role is documented with all variables, please refer to the documentation f
 
 ## Roles documentation
 
+> [!NOTE]
+> Some roles have fixed requirements that you must observe. Please have a look at the [requirements](docs/01-requirements.md) before using the collection. (There is a high probability that some of them will be refactored soon)
+
 * [Beats](docs/role-beats.md)
 * [Elasticsearch](docs/role-elasticsearch.md)
 * [Kibana](docs/role-kibana.md)

docs/01-requirements.md

@@ -0,0 +1,11 @@
+# Requirements
+
+There are some requirements that the user have to fulfill while using the collection. Some of them will be refactored and disappear from the list soon.
+
+**Inventory names**
+
+The collection provides roles for several tools (elasticsearch, kibana, ...). In some tasks hosts from the specific inventory group are fetched. The group names are customizable via variables. But using different inventory names than provided inside the variables will result in errors.
+
+**elasticstack_ca_host**
+
+This is a mandatory variable. It is used to define the host that will be used as "CA host".