Add status badge for CI actions (#116)

Signed-off-by: mgodwan <mgodwan@amazon.com>
(cherry picked from commit 6eb028f)
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

README.md

@@ -1,3 +1,6 @@
+[![Backward Compatibility Checks](https://github.com/opensearch-project/custom-codecs/actions/workflows/ci.yml/badge.svg?branch=main)](https://github.com/opensearch-project/custom-codecs/actions/workflows/ci.yml)
+[![Publish snapshots to maven](https://github.com/opensearch-project/custom-codecs/actions/workflows/publish-maven-snapshots.yml/badge.svg?branch=main)](https://github.com/opensearch-project/custom-codecs/actions/workflows/publish-maven-snapshots.yml)
+
 # Custom Codecs
 Custom Codecs plugin makes it possible for users to provide custom Lucene codecs for loading through Apache Lucene's `NamedSPILoader`.
 These codecs can be used to customize the on-disk representation of the opensearch indexes. For example, zstd compression can be used for