doc: add simple readme (#35)

Author: tdejager

README.md

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+# Pixi Build Backends
+
+**Work in Progress: Backend Implementations for Building Pixi Projects from Source**
+
+This repository contains backend implementations designed to facilitate the building of pixi projects directly from their source code. These backends aim to enhance the functionality of Pixi, a cross-platform, multi-language package manager and workflow tool built on the foundation of the conda ecosystem.
+
+## Available Build Backends
+The idea is that a backend should be able to build a certain type of so
+The repository provides the following build backends:
+
+1. **pixi-build-python**: A backend tailored for building Python-based projects.
+2. **pixi-build-cmake**: A backend designed for projects utilizing CMake as their build system.
+3. **pixi-build-rattler-build**: A backend for building [`recipe.yaml`](https://rattler.build/latest/) directly
+
+These backends are located in the `crates/*` directory of the repository.
+
+## Features
+* **Backend Implementations**: Provides the necessary components to build Pixi projects from source, integrating seamlessly with the Pixi ecosystem.
+* **Schema Definitions**: Includes schema definitions to standardize and validate project configurations.
+
+## Getting Started
+
+**Note**: This project is currently a work in progress. Functionality and documentation are under active development.
+All of these backends are directly uploaded to the [Pixi Build Backends](https://prefix.dev/channels/pixi-build-backends).
+So will be utilized in pixi directly. We want to move these to conda-forge eventually.
+
+For example, this `build-section` will use the python backend to build a python project:
+
+```toml
+[build-system]
+# The name of the build backend to use. This name refers both to the name of
+# the package that provides the build backend and the name of the executable
+# inside the package that is invoked.
+#
+# The `build-backend` key also functions as a dependency declaration. At least
+# a version specifier must be added.
+build-backend = { name = "pixi-build-python", version = "*" }
+# These are the conda channels that are used to resolve the dependencies of the
+# build backend package.
+channels = [
+  "https://prefix.dev/pixi-build-backends",
+  "https://prefix.dev/conda-forge",
+]
+```
+
+
+### Developing on Backends
+
+Even though binary versions are available on the prefix channels, its also quite easy to get started on developing a new backend or work on an existing one.
+To start development make sure you have installed [pixi](https://pixi.sh). After which, a number of command should be available:
+
+```bash
+# To build the backens
+pixi run build
+# .. to install a backend, for example the python one:
+pixi r install-pixi-build-python
+```
+
+You can make use of these backends to overwrite any existing backend in pixi. For example, to overwrite the python backend with a local version, you can do the following:
+
+```bash
+PIXI_BUILD_BACKEND_OVERRIDE=/path/to/pixi-build-python pixi install
+```
+
+## Contributing
+Contributions are welcome! Please refer to the contributing guidelines for more information.
+License
+
+This project is licensed under the BSD-3-Clause License. See the LICENSE file for details.
+Acknowledgements
+
+## Acknowledgemts
+Developed by prefix.dev.
+For more information about Pixi and related projects, visit the [prefix-dev](https://github.com/prefix-dev) organization on GitHub.