docs: add alias context to uv tool run --help command (astral-sh#7695)

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## Summary

<!-- What's the purpose of the change? What does it do, and why? -->
- Adds detail to the `uv tool run --help` CLI that lets users know about
the shorthand, `uvx`

## Test Plan

<!-- How was it tested? -->
Building and running CLI
```
…📝✓] via 🐋 orbstack via 🎁 v0.4.16 via  pyenv via ⚙️ v1.81.0on ☁️  (us-east-2) took 3s 
➜ ./target/debug/uv tool run --help
Run a command provided by a Python package. Also available via the alias `uvx`.

Usage: uv tool run [OPTIONS] [COMMAND]

...

You can also use `uvx` as an alias for `uv tool run`. 
Use `uv help tool run` for more details.
```

---------

Co-authored-by: Zanie Blue <[email protected]>

crates/uv-cli/src/lib.rs

@@ -3262,6 +3262,11 @@ pub enum ToolCommand {
     ///
     /// Packages are installed into an ephemeral virtual environment in the uv
     /// cache directory.
+    #[command(
+        after_help = "Use `uvx` as a shortcut for `uv tool run`.\n\n\
+        Use `uv help tool run` for more details.",
+        after_long_help = ""
+    )]
     Run(ToolRunArgs),
     /// Hidden alias for `uv tool run` for the `uvx` command
     #[command(