[BUG] readme doesn't point to documentation

[drBenway]

Describe the bug
readme.md: the links for project and documentation point to https://opensearch.org/. I would expect 2 dedicated pages

To Reproduce
Steps to reproduce the behavior:

1. Go to https://github.com/opensearch-project/logstash-output-opensearch
2. Click on 'project website' and 'documentation' links under the "Project resources" topic
3. I see the opensearch.org page

Expected behavior
Have 2 distinct pages and a detailed documentation for the plugin setup

Plugins
NA

Screenshots
NA

Host/Environment (please complete the following information):

• OS: Linux Mint
• Version 21
• latest Firefox

Additional context
NA