Update documentation links for version 18 in readme

Author: Andriciuc

README.md

@@ -13,14 +13,14 @@ Percona Server for PostgreSQL is an open source binary-compatible drop-in replac
 
 Percona Server and upstream PostgreSQL function identically enabling you to migrate from one to another. 
 
-This repository contains the source files for [Percona Distribution for PostgreSQL documentation](https://www.percona.com/doc/postgresql/17/index.html). The documentation is written in [Markdown](https://www.markdownguide.org/) markup language and is created using [MkDocs Documentation Generator](https://www.mkdocs.org/). 
+This repository contains the source files for [Percona Distribution for PostgreSQL documentation](https://www.percona.com/doc/postgresql/18/index.html). The documentation is written in [Markdown](https://www.markdownguide.org/) markup language and is created using [MkDocs Documentation Generator](https://www.mkdocs.org/). 
 
 ## Contributing
 
 We welcome all contributions and are always looking for new members that are as dedicated to serving the community as we are. You can reach out to us using our [forums ](https://forums.percona.com/c/postgresql/25) and [Jira issue tracker ](https://jira.percona.com/projects/DISTPG/issues/DISTPG-16?filter=allopenissues). 
 
-For how to contribute to documentation, read the [Contributing guide ](https://github.com/percona/postgresql-docs/blob/17/CONTRIBUTING.md).
+For how to contribute to documentation, read the [Contributing guide ](https://github.com/percona/postgresql-docs/blob/18/CONTRIBUTING.md).
 
 ## License
 
-Percona Distribution for PostgreSQL documentation is licensed under the [PostgreSQL license ](https://opensource.org/licenses/postgresql).
+Percona Distribution for PostgreSQL documentation is licensed under the [PostgreSQL license ](https://opensource.org/licenses/postgresql).