Write a descriptive README with a quick-start example and docs link

README.md

@@ -1,2 +1,57 @@
 # valentBind
-The multivalent binding model implemented in Python.
+
+[![Test](https://github.com/meyer-lab/valentBind/actions/workflows/pytest.yml/badge.svg)](https://github.com/meyer-lab/valentBind/actions/workflows/pytest.yml)
+[![Code Quality](https://github.com/meyer-lab/valentBind/actions/workflows/code-quality.yml/badge.svg)](https://github.com/meyer-lab/valentBind/actions/workflows/code-quality.yml)
+[![Docs](https://github.com/meyer-lab/valentBind/actions/workflows/docs.yml/badge.svg)](https://meyer-lab.github.io/valentBind/)
+[![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](LICENSE)
+
+`valentBind` is a Python implementation of a multivalent binding model:
+it computes how much ligand and receptor end up bound at equilibrium
+when multivalent ligand complexes (e.g., antibodies, cytokine
+complexes, or other multi-headed binders) interact with one or more
+receptor types on a cell surface, accounting for avidity effects from
+multiple simultaneous bonds. It's used across several projects in the
+[Meyer Lab](https://github.com/meyer-lab) to model antibody Fc-receptor
+and cytokine-receptor binding.
+
+**[Full documentation and API reference](https://meyer-lab.github.io/valentBind/)**
+
+## Installation
+
+```bash
+pip install git+https://github.com/meyer-lab/valentBind.git
+```
+
+## Quick start
+
+There are two entry points, depending on whether your ligand complexes
+are all identical (`polyfc`) or drawn from a mixture of different
+complex compositions (`polyc`).
+
+```python
+from valentbind import polyfc
+
+L0 = 1e-9  # concentration of ligand complexes (M)
+KxStar = 1e-12  # detailed-balance-corrected cross-linking constant
+f = 4  # valency of the ligand complex
+Rtot = [1e5]  # total abundance of each receptor type on the cell
+LigC = [1.0]  # relative composition of monomer ligands in the complex
+Kav = [[1e6]]  # monomer ligand/receptor affinity matrix (ligands x receptors)
+
+Lbound, Rbound, vieq, Rmulti_n = polyfc(L0, KxStar, f, Rtot, LigC, Kav)
+```
+
+See the [docs](https://meyer-lab.github.io/valentBind/) for the full
+API reference (including `polyc`, for mixtures of heterogeneous
+complexes) and the [`examples/`](examples/) directory for complete
+plotting scripts.
+
+## Development
+
+```bash
+git clone https://github.com/meyer-lab/valentBind.git
+cd valentBind
+uv sync
+make test   # run the test suite
+uv run ruff check .   # lint
+```