Merge pull request #6 from tweag/readme

Rewrite README

README.md

@@ -1,3 +1,31 @@
-# Introduction
+# Genealogos
+The Genealogos project is a tool that takes output from Nix evaluation tools
+and produces SBOM files. Currently, it takes input from [nixtract][nixtract]
+and produces json output compliant with the [CycloneDX][cyclonedx] 1.5
+specification. Output from Genealogos can be used by various other tools to
+perform further analysis. Any tool that takes JSON in the CycloneDX format
+should accept Genealogos' output.
 
-Genealogos is a project to leverage the nixpkgs project to generate CycloneDX SBOMs files, and easy to read HTML SBOM reports.
+The project is still very early stages, so the output may as of yet be of little
+use.
+
+## Using Genealogos
+This section assumes you are using the latest `main` version version of [nixtract][nixtract].
+
+### Analyzing a package from your system nixpkgs channel
+```fish
+nixtract --target-attribute-path hello - | genealogos
+```
+
+### Analyzing a local flake
+```fish
+nixtract --target-flake-ref /path/to/your/local/flake - | genealogos
+```
+
+For more `nixtract` arguments, see `nixtract --help`.
+
+## Building Genealogos
+`nix build` or `cargo build`. A development shell is present via `nix devel`.
+
+[cyclonedx]: https://cyclonedx.org/
+[nixtract]: https://github.com/tweag/nixtract/