Update project description in README.md

• Provide links to more related resources (BSSD, Lanelet)
• Expand on the project description (The purpose of the project should be clear to an outsider)
• Dependencies: Add short description of include purpose.
• How to build the library (Shared/Static)
• Using the library using CMake
  • Add CMake FetchContent support
• Populate the Code Example block with a simple example