docs: update cli docs for duckdb instructions (#821)

Closes #820

Author: gadomski

crates/cli/README.md

@@ -10,10 +10,20 @@ Command Line Interface (CLI) for [STAC](https://stacspec.org/), named `rustac`.
 
 ## Installation
 
+If you have DuckDB on your system:
+
+```sh
+cargo install rustac
+```
+
+> [!TIP]
+> Set `DUCKDB_LIB_DIR` to the directory containing your **libduckdb**.
+> If you're on macos and using [Homebrew](https://brew.sh/), this might be `export DUCKDB_LIB_DIR=/opt/homebrew/lib`
+
+Otherwise:
+
 ```sh
-cargo install rustac -F duckdb  # to use libduckdb on your system
-# or
-cargo install rustac -F duckdb-bundled  # to build libduckdb on install (slow)
+cargo install rustac -F duckdb-bundled  # (slow)
 ```
 
 Then:
@@ -55,17 +65,6 @@ $ rustac validate item.json
 
 Use the `--help` flag to see all available options for the CLI and the subcommands:
 
-## Features
-
-This crate has three features:
-
-- `pgstac`: enable a [pgstac](https://github.com/stac-utils/pgstac) backend for `rustac serve`
-- `duckdb`: build with DuckDB support, which enables searching [stac-geoparquet](https://github.com/stac-utils/stac-geoparquet) (requires DuckDB to be present on your system)
-- `duckdb-bundled`: bundle DuckDB by building it from source, instead of using a local installation (does _not_ require DuckDB to be present on your system)
-
-> [!TIP]
-> If you're using the `duckdb` feature, set `DUCKDB_LIB_DIR` to the directory containing your **libduckdb**. If you're on macos and using [Homebrew](https://brew.sh/), this might be `export DUCKDB_LIB_DIR=/opt/homebrew/lib`
-
 ## Other info
 
 This crate is part of the [rustac](https://github.com/stac-utils/rustac) monorepo, see its README for contributing and license information.