Update build-toolchain.sh and README.md for toolchain environment script changes

- Modified build-toolchain.sh to copy env.sh from the scripts directory instead of the top-level directory, ensuring proper organization.
- Updated README.md to reflect the new version of uClibc-ng and clarify the structure of the output archive, including the location of env.sh within the archive.

build-toolchain.sh

@@ -220,7 +220,7 @@ trap 'rm -rf "$WDIR"' EXIT
 ARCHIVE_TOOLCHAIN_DIR="${WDIR}/${TARGET}"
 mkdir -p "${ARCHIVE_TOOLCHAIN_DIR}"
 cp -a "${INSTALL_DIR}"/* "${ARCHIVE_TOOLCHAIN_DIR}/"
-cp -a "${TOP}/env.sh" "${WDIR}/env.sh"
+cp -a "${TOP}/scripts/env.sh" "${WDIR}/env.sh"
 
 find "${ARCHIVE_TOOLCHAIN_DIR}" -type f -executable -exec strip -p {} \; 2>/dev/null || true