Document usage

The usage of the tool has been documented in the README. A rough
explanation of the test hierarchy has been added for better
understanding as well.

Justfile

@@ -2,13 +2,13 @@
 _default:
     just --list
 
-format ARGS:
+format *ARGS:
     cargo fmt --all -- {{ARGS}}
 
 lint:
     cargo clippy --all-targets --all-features -- -D warnings
 
-run ARGS:
+run *ARGS:
     cargo run -- {{ARGS}}
 
 test:

README.md

@@ -1,7 +1,62 @@
 # ✔️ Smoke Tests for Rust Infrastructure
 
 This repository contains a collection of smoke tests for the infrastructure of
-the [Rust] project.
+the [Rust] project. The tests mostly check that the Content Delivery Networks
+that the project uses for its releases and crates return the expected responses.
+
+```shell
+$ just run
+✅ crates.io
+  ✅ rust-lang/crates.io#4891 - Encoded + character
+    ✅ CloudFront encoded
+    ✅ CloudFront unencoded
+    ✅ CloudFront with space
+    ✅ Fastly encoded
+    ✅ Fastly unencoded
+    ✅ Fastly with space
+  ✅ rust-lang/crates.io#6164 - CORS headers
+    ✅ CloudFront
+    ✅ Fastly
+  ✅ Database dumps
+    ✅ CloudFront
+    ✅ Fastly
+
+✅ rustup
+  ✅ rustup.sh
+    ✅ CloudFront
+    ✅ Fastly
+  ✅ win.rustup.rs
+    ✅ aarch64
+    ✅ i686
+    ✅ x86_64
+```
+
+## Usage
+
+This project uses [Just](https://github.com/casey/just) as a command runner. It
+is recommended to install and use it with this project, but the commands that
+`just` runs can also be copied from the [Justfile](./Justfile) at the root of
+the repository.
+
+The smoke tests can be run with the following command:
+
+```shell
+just run
+```
+
+The smoke tests are organized in the following way:
+
+- _Test suites_ execute tests for a specific service, for example `crates.io`
+  or`rustup`.
+- Each test suite has one or more _test groups_, which are collections of tests
+  that check a specific aspect of the service. Usually, they correspond to a
+  feature or a bug that was fixed in the past.
+- Each test group has one or more _tests_, which usually execute a single HTTP
+  request and check the response. A common pattern is to have a test for each
+  CDN, for example.
+
+If a test fails, the test failure and its error message will be bubbled up the
+chain and mark the whole test suite as failed.
 
 ## Development
 
@@ -21,8 +76,10 @@ pre-commit install
 
 Licensed under either of
 
-- Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE) or <http://www.apache.org/licenses/LICENSE-2.0>)
-- MIT license ([LICENSE-MIT](LICENSE-MIT) or <http://opensource.org/licenses/MIT>)
+- Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE)
+  or <http://www.apache.org/licenses/LICENSE-2.0>)
+- MIT license ([LICENSE-MIT](LICENSE-MIT)
+  or <http://opensource.org/licenses/MIT>)
 
 at your option.