Improve getting started guide (flexivian.github.io/flexbench) - general improvements

[iskitsas]

Review all the pages and make sure the provided info there:

• is clear
• the scripts and examples are working
• is easy for a new joiner to follow

Fix typos

Focus on restructuring the pages to help someone understand the build process for all the 3 apps:

• nodejs script
• desktop-app
• server-app

Provide clear example of usage for all the 3 apps

Provide a GSoC > 2024 page to keep a track of work during the 2024 Google Summer of Code (do not delete the previous page for GSoC2024)

If needed we will split the work in smaller issues, keeping a reference (in comments) with this issue as a parent. For any split issue do not forget to add the labels:

• gsoc24
• improve-getting-started-guide