Add a quick start to the book (google#202)

book/src/SUMMARY.md

@@ -6,6 +6,8 @@
     - [Terminology](overview/terminology.md)
     - [Features](overview/features.md)
 
+- [Quick start](quick/README.md)
+
 - [Applet user guide](applet/README.md)
     - [Setup](applet/setup.md)
     - [Create a new applet](applet/create.md)

book/src/quick/README.md

@@ -0,0 +1,39 @@
+# Quick start
+
+## Repository setup
+
+Clone the repository and run the setup script:
+
+```sh
+git clone https://github.com/google/wasefire
+cd wasefire
+./scripts/setup.sh
+```
+
+The setup script is best effort. When possible, it will directly invoke
+installation commands, possibly asking for sudo password. Otherwise, it will
+return an error and print a message about the next manual step. Once the problem
+is addressed, the script must be run again. The script will eventually return a
+success code indicating that no manual step is required and everything seems in
+order.
+
+## Run an applet
+
+If you don't have a Nordic board, you can run applets on your desktop:
+
+```sh
+cargo xtask applet assemblyscript hello runner host
+```
+
+If you have an nRF52840 dev-kit, you can also run applets on the board:
+
+```sh
+cargo xtask applet rust blink runner nordic
+```
+
+The general format is `cargo xtask applet LANGUAGE NAME runner BOARD`. Example
+applets are listed in the `examples` directory by _language_ then _name_.
+_Boards_ are listed under the `crates` directory and are prefixed by `runner-`.
+
+Feel free to stop and play around by directly editing the examples. Or continue
+reading for a deeper tutorial on how to write applets in Rust.

crates/xtask/src/main.rs

@@ -22,7 +22,7 @@ use std::path::Path;
 use std::process::{Command, Output};
 use std::str::FromStr;
 
-use anyhow::{ensure, Context, Result};
+use anyhow::{bail, ensure, Context, Result};
 use clap::Parser;
 use lazy_static::lazy_static;
 use probe_rs::config::TargetSelector;
@@ -257,7 +257,7 @@ impl AppletOptions {
         match self.lang.as_str() {
             "rust" => self.execute_rust(main),
             "assemblyscript" => self.execute_assemblyscript(main),
-            _ => panic!("unsupported language"),
+            x => bail!("unsupported language {x}"),
         }
     }