Docs: add contributor guidelines for issue assignment and Website WG

[anish-devgit]

Description

This Pull Request adds a new Contributing section to the README.rst file. These updates provide clearer guidance for new community members and streamline the onboarding process by documenting the repository's specific workflow, as discussed in #2375.

Key Changes

• Website Working Group (WG) Approval: Clarifies that the WG triages issues and should approve them before a Pull Request is submitted.
• Issue Assignment Policy: Explicitly states that the GitHub "Assignee" field is not used, helping to set correct expectations for new contributors.
• Workflow Best Practices: Provides a simple 3-step guide for claiming issues via comments to prevent duplicate work and overlapping PRs.

Related Issues

Fixes #2375

[SaptakS]

Hi @anish-devgit thanks for creating this PR! There are few internal Website working group discussions related to contribution guidelines and issue triaging . A contributor guidelines is definitely very important, and I am hoping to add one after discussing with the rest of the group. I really do appreciate your work but I will probably currently not review (or have an answer how to proceed) before the internal discussions.