docs: update links to contributing guides

First, the worflow and backend_tests guides were merged together,
so delete the link to the one of them.

Second, these links were going to the 3.2.0 docs,
so update to the new path.

Author: NickCrews

docs/CONTRIBUTING.md

@@ -4,8 +4,7 @@ We love new contributors!
 
 To get started:
 
-1. [Set up a development environment](https://ibis-project.org/docs/latest/contribute/01_environment/)
-1. [Learn about the commit workflow](https://ibis-project.org/docs/latest/contribute/02_workflow/)
-1. [Review the code style guidelines](https://ibis-project.org/docs/latest/contribute/03_style/)
-1. [Learn how to run the backend test suite](https://ibis-project.org/docs/latest/contribute/04_backend_tests/)
-1. [Dig into the nitty gritty of being a maintainer](https://ibis-project.org/docs/latest/contribute/05_maintainers_guide/)
+1. [Set up a development environment](https://ibis-project.org/docs/latest/community/contribute/01_environment/)
+1. [Learn about the commit workflow](https://ibis-project.org/docs/latest/community/contribute/02_workflow/)
+1. [Review the code style guidelines](https://ibis-project.org/docs/latest/community/contribute/03_style/)
+1. [Dig into the nitty gritty of being a maintainer](https://ibis-project.org/docs/latest/community/contribute/05_maintainers_guide/)