docs: add repository anatomy section to contribute-to-precice page

[praaatap]

PR Description: Add Repository Anatomy to preCICE Contributing Guide

Title: docs: add repository anatomy section to contribute-to-precice page

Description:

This PR adds a comprehensive Repository Anatomy subsection to the "Contributing code" section on the "Contribute to preCICE" page. This section will provide a detailed overview of the precice/precice core code repository structure to help new contributors understand the code structure and the whereabouts of specific functionalities.

Key Changes:

• Directory Tree Overview: A visual representation of the project root directory has been added.
• Detailed src/ modularization: An explanation of every single src/ subdirectory has been provided, including acceleration, com, mapping, mesh, etc.
• Support for Infrastructure: An explanation of the tests/, docs/, cmake/, tools/, benchmarks/, examples/, extras/, thirdparty/, and .github/ directories has been provided.
• Root-level Reference: An explanation of the root-level configuration files has been provided, including CMake configuration, formatting, and CI scripts.
• Branching Model: An explanation of the develop and main branch usage has been provided.
• Ecosystem Links: An explanation of the core library's relation to the larger preCICE organization has been provided.

Impact:
This will increase transparency and help new contributors overcome the entry barrier.

Modified File:

• content/community/contribute/community-contribute-to-precice.md