docs: correct the README and add installation examples

[philomath213]

The README had drifted from how the project actually builds and installs.

• Removes three dead badges (the Linux/MacOS/Windows Package workflows were deleted in Support Python 3.13 and introduce pypa/cibuildwheel #509) and a dead logo link (duet.openmined.org returns 404)
• Corrects the build-from-source section: there are no git submodules, no protobuf compiler to install, and no manual SEAL build on Windows — CMake fetches and builds everything
• States supported Python versions (3.11–3.14) and the wheel/platform matrix, and mentions the sdist and the numpy dependency
• Documents two build failures users currently hit with no explanation: CMake 4.x needs CMAKE_POLICY_VERSION_MINIMUM=3.5, and Xcode 16+ cannot compile the vendored xtensor
• Adds uv and conda examples for anyone whose Python is older than 3.11
• Replaces the Docker and Bazel sections with TODO notes: the images are unmaintained since 2021 (v0.3.4) and the Bazel build is broken

All links verified resolving.