docs: update installation instructions to reference prqlc-cli

The CLI was extracted into the separate prqlc-cli crate. Update:
- prqlc/prqlc/README.md: cargo install now references prqlc-cli, intro
  and CLI section clarify that the CLI is a separate crate
- web/website/content/_index.md: crates.io link and cargo install
  command updated to prqlc-cli

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: snth

prqlc/prqlc/README.md

@@ -1,15 +1,17 @@
 # PRQL compiler
 
 `prqlc` is the reference implementation of a compiler from PRQL to SQL, written
-in Rust. It also serves as the CLI.
+in Rust. The CLI is provided by the separate
+[`prqlc-cli`](https://crates.io/crates/prqlc-cli) crate (binary name remains
+`prqlc`).
 
 For more on PRQL, check out the [PRQL website](https://prql-lang.org) or the
 [PRQL repo](https://github.com/PRQL/prql).
 
 ## CLI
 
-`prqlc` serves as a CLI for the PRQL compiler. It is a single, dependency-free
-binary that compiles PRQL into SQL.
+The CLI is provided by the [`prqlc-cli`](https://crates.io/crates/prqlc-cli)
+crate. It is a single, dependency-free binary that compiles PRQL into SQL.
 
 ## Usage
 
@@ -97,12 +99,12 @@ Precompiled binaries are available for Linux, macOS, and Windows on the
 
 ```sh
 # From crates.io
-cargo install prqlc
+cargo install prqlc-cli
 ```
 
 ```sh
 # From a local PRQL repository
-cargo install --path prqlc/prqlc
+cargo install --path prqlc/prqlc-cli
 ```
 
 ### Shell completions

web/website/content/_index.md

@@ -153,12 +153,12 @@ tools_section:
 
         `pip install pyprql`
 
-    - link: https://crates.io/crates/prqlc
+    - link: https://crates.io/crates/prqlc-cli
       label: "prqlc"
       text: |
         A CLI for PRQL compiler, written in Rust.
 
-        `cargo install prqlc`
+        `cargo install prqlc-cli`
 
         `brew install prqlc`