Add more context to the README (#29)

- Add Birdcage logo and badges
- Explain original purpose for Birdcage
- Document the technologies used by Birdcage
- Avoid "Do not use Birdcage" language
- Update explanation for sandbox example

Co-authored-by: Christian Dürr <102963075+cd-work@users.noreply.github.com>
Co-authored-by: Charles Coggins <maxrake@users.noreply.github.com>

README.md

@@ -1,29 +1,70 @@
 # Birdcage
 
+<div align="center">
+
+[![GitHub](https://img.shields.io/github/license/phylum-dev/birdcage)][license]
+[![GitHub issues](https://img.shields.io/github/issues/phylum-dev/birdcage)][issues]
+[![Contributor Covenant](https://img.shields.io/badge/Contributor%20Covenant-2.1-4baaaa.svg)][CoC]
+[![Discord](https://img.shields.io/discord/1070071012353376387?logo=discord)][discord_invite]
+[![Crate](https://img.shields.io/crates/v/birdcage)](https://crates.io/crates/birdcage)
+[![Documentation](https://docs.rs/birdcage/badge.svg)](https://docs.rs/birdcage)
+
+[license]: https://github.com/phylum-dev/birdcage/blob/main/LICENSE
+[issues]: https://github.com/phylum-dev/birdcage/issues
+[CoC]: https://github.com/phylum-dev/birdcage/blob/main/CODE_OF_CONDUCT.md
+[discord_invite]: https://discord.gg/Fe6pr5eW6p
+
+[![Birdcage logo](./assets/Birdcage.png)][protection]
+
+</div>
+
 ## About
 
 Birdcage is a cross-platform embeddable sandboxing library allowing restrictions
 to Filesystem and Network operations using native operating system APIs.
 
-Birdcage **is not** a complete sandbox preventing all side-effects or permanent
-damage. Applications can still execute most system calls, which is especially
-dangerous when execution is performed as root. Do not use Birdcage as a safety
-barrier for known-malicious code and keep other security mechanisms like user
-restrictions in place.
+Birdcage was originally developed for use by the [Phylum CLI] as an extra layer
+of [protection] against potentially malicious dependencies (see the [blog post]
+for details). To better protect yourself from these security risks, [sign up
+now]!
+
+[phylum cli]: https://github.com/phylum-dev/cli
+[protection]: https://www.phylum.io/defend-developers
+[blog post]: https://blog.phylum.io/sandboxing-package-installations-arms-developers-with-defense-against-open-source-attacks-and-unintended-consequences/
+[sign up now]: https://www.phylum.io/
+
+Birdcage focuses **only** on Filesystem and Network operations. It **is not** a
+complete sandbox preventing all side-effects or permanent damage. Applications
+can still execute most system calls, which is especially dangerous when
+execution is performed as root. Birdcage should be combined with other security
+mechanisms, especially if you are executing known-malicious code.
 
-## Usage
+## Example
 
-You can run applications inside Birdcage's sandbox by running the `sandbox`
-example:
+An example for using Birdcage's API can be found in `./examples/sandbox`, which
+runs an application with CLI-configurable restrictions applied.
+
+Trying to run without any exceptions will produce an error:
+
+```bash
+$ cargo run --example sandbox -- echo "Hello, Sandbox\!"
+Error: Os { code: 13, kind: PermissionDenied, message: "Permission denied" }
+```
+
+Running the same command with explicit permissions allows execution:
 
 ```bash
-cargo run --example sandbox -- -e /usr/bin/echo -e /usr/lib echo "Hello, Sandbox\!"
+$ cargo run --example sandbox -- -e /usr/bin/echo -e /usr/lib echo "Hello, Sandbox\!"
+Hello, Sandbox!
 ```
 
 Check out `cargo run --example sandbox -- --help` for more information on how to
 use the example.
 
 ## Supported Platforms
 
- - Linux (5.13+)
- - macOS
+ - Linux (5.13+) via [Landlock] and [seccomp]
+ - macOS via `sandbox_init()` (aka Seatbelt)
+
+[landlock]: https://www.kernel.org/doc/html/latest/userspace-api/landlock.html
+[seccomp]: https://man7.org/linux/man-pages/man2/seccomp.2.html