updated compatibility information (#189)

* updated compatibility information
added row on table relating to the 2.x version of the client
added updated policy information regarding compatibility

Signed-off-by: Abhinav Garg <ag90@illinois.edu>

* Update opensearch/src/lib.rs

Co-authored-by: Andriy Redko <drreta@gmail.com>
Signed-off-by: Abhinav Garg <112351850+AbhinavGarg90@users.noreply.github.com>

* added exception warning

Signed-off-by: Abhinav Garg <ag90@illinois.edu>

* Update opensearch/src/lib.rs

fixed typo

Co-authored-by: Thomas Farr <xtansia@xtansia.com>
Signed-off-by: Abhinav Garg <112351850+AbhinavGarg90@users.noreply.github.com>

---------

Signed-off-by: Abhinav Garg <ag90@illinois.edu>
Signed-off-by: Abhinav Garg <112351850+AbhinavGarg90@users.noreply.github.com>
Co-authored-by: Andriy Redko <drreta@gmail.com>
Co-authored-by: Thomas Farr <xtansia@xtansia.com>

opensearch/src/lib.rs

@@ -23,9 +23,11 @@
 //!
 //! # Versions and Compatibility
 //!
-//! | Rust client | OpenSearch |
+//! | Rust client | OpenSearch    |
 //! |-------------|---------------|
 //! | 1.x         | 1.x           |
+//! | 2.x         | 2.x, 1.x^     |
+//! - ^: With the exception of some previously deprecated APIs 
 //!
 //! A major version of the client is compatible with the same major version of OpenSearch.
 //! Since OpenSearch is developed following [Semantic Versioning](https://semver.org/) principles,
@@ -42,6 +44,10 @@
 //! In the latter case, a 1.4.0 client won't contain API functions for APIs that are introduced in
 //! OpenSearch 1.5.0+, but for all other APIs available in OpenSearch, the respective API
 //! functions on the client will be compatible.
+//! 
+//! In some instances, a new major version of OpenSearch may remain compatible with an
+//! older major version of the client, which may not warrant a need to update the client.
+//! Please consult COMPATIBILITY.md for more details.
 //!
 //! **No compatibility assurances are given between different major versions of the client and
 //! OpenSearch**. Major differences likely exist between major versions of OpenSearch, particularly