docs(readme): rework for users — quickstart first, tasks over flags (#207)

The README was a flag-by-flag reference manual with maintainer content mixed in. Restructured around what a new user does: install, a runnable quickstart (real public parquet, three commands to a query result), then task-oriented tours — getting data in (connect vs import, stated as a choice for the first time), query/explore, cross-source joins, search, scripting/agents. Per-flag detail defers to --help and the bundled skills; the Releasing section moves to docs/RELEASING.md; the version badge tracks releases instead of a hardcoded number.

Co-authored-by: Eddie A Tejeda <669988+eddietejeda@users.noreply.github.com>

Author: eddietejeda