[DOCS] Adds compatibility matrix to the docs and readme (#8045)

* [DOCS] Adds compatibility matrix to the docs and readme.

* Apply suggestions from code review

* Update README.md

* Apply suggestions from code review

Author: szabosteve

README.md

@@ -17,10 +17,20 @@ The .NET client for Elasticsearch provides strongly typed requests and responses
 
 ## Compatibility
 
-Language clients are forward compatible; meaning that clients support
-communicating with greater or equal minor versions of Elasticsearch.
-Elasticsearch language clients are only backwards compatible with default
-distributions and without guarantees made.
+Language clients are forward compatible; meaning that the clients support
+communicating with greater or equal minor versions of Elasticsearch without
+breaking. It does not mean that the clients automatically support new features
+of newer Elasticsearch versions; it is only possible after a release of a new
+client version. For example, a 8.12 client version won't automatically support
+the new features of the 8.13 version of Elasticsearch, the 8.13 client version
+is required for that. Elasticsearch language clients are only backwards
+compatible with default distributions and without guarantees made.
+
+| Elasticsearch Version | Elasticsearch-NET Branch  | Supported |
+| --------------------- | ------------------------- | --------- |
+| main                  | main                      |           |
+| 8.x                   | 8.x                       | 8.x       |
+| 7.x                   | 7.x                       | 7.17      |
 
 ## Installation
 

docs/install.asciidoc

@@ -58,12 +58,25 @@ To learn how to connect the {es} client, refer to the <<connecting,Connecting>>
 === Compatibility
 
 The {es} client is compatible with currently maintained .NET runtime versions. 
-Compatibility with End of Life (EOL) .NET runtimes is not guaranteed or supported.
-
-Language clients are forward compatible; meaning that clients support 
-communicating with greater or equal minor versions of {es}. {es} language 
-clients are only backward compatible with default distributions and without 
-guarantees made.
+Compatibility with End of Life (EOL) .NET runtimes is not guaranteed or
+supported.
+
+Language clients are forward compatible; meaning that the clients support
+communicating with greater or equal minor versions of {es} without breaking. It
+does not mean that the clients automatically support new features of newer
+{es} versions; it is only possible after a release of a new client version. For
+example, a 8.12 client version won't automatically support the new features of
+the 8.13 version of {es}, the 8.13 client version is required for that. {es}
+language clients are only backwards compatible with default distributions and
+without guarantees made.
+
+|===
+| Elasticsearch Version | Elasticsearch-NET Branch  | Supported
+
+| main                  | main                      | 
+| 8.x                   | 8.x                       | 8.x
+| 7.x                   | 7.x                       | 7.17
+|===
 
 Refer to the https://www.elastic.co/support/eol[end-of-life policy] for more 
 information.