docs: simplify README and keep release version synchronized

[YiChengZQZ]

Summary

The README still described a previous, published version as a planned release and mixed installation instructions with long implementation examples. Replace it with a consistent short guide: a one-line latest release, installation, API Key/RSA example links, concise upgrade notes, and support.

Move Meter transport instructions into docs/meter-event-upload.md and preserve Java migration details in a separate guide where applicable. Update scripts/set-version.sh to keep the new release line synchronized during version bumps. SDK runtime code, package versions, and CHANGELOG are unchanged.

Validation

• Fetched origin/master and merged it into this documentation branch before validation (already up to date).
• git diff --check and shell syntax checks passed.
• Checked relative documentation links, balanced code fences, and absence of stale planned/unpublished wording in README.
• Ran the updated version script with a synthetic version in a temporary copy; the README release line updated successfully.
• No runtime build was run: changes are documentation and version-script formatting only.

Please review and merge manually.