Improve 'Before you Begin' documentation and its visibility

[jld01]

Based on discusssion on the CDT project call 2026-04-08, we should improve our documentation for the installation of necessary tools for native application development in CDT and make it more visible to new users. Improvements to include:

• Linking to the Before you Begin documentation page from the top-level README file.
• Adding native tool installation instructions for prominent Linux distributions using apt and dnf