[SRombauts]

Summary

• Document the actively developed C++17/SQLiteCpp 4.x line and the C++11-compatible sqlitecpp-3.x maintenance line, with a direct branch link.
• Clarify that 3.x starts from 3.4.0, retains the SQLite 3.8.7 baseline, and targets compatible fixes/backports (with some optional C++14 headers).
• Distinguish the historical sqlitecpp-3.4.x branch from the ongoing 3.x maintenance branch.
• Remove outdated C++11/SQLite compatibility notes embedded inside the goals list, and scope the platform requirements to master.

Validation

Documentation-only change; reviewed branch URLs and the 3.x branch README/CMake baseline.

[coveralls]

coverage: 99.716%. remained the same — fix-readme-cpp11-maintenance into master