chore: add usage/install to readme

README.md

@@ -1,9 +1,56 @@
 # Maximum genetic component phenotyping
 
 [![Ruff](https://img.shields.io/endpoint?url=https://raw.githubusercontent.com/astral-sh/ruff/main/assets/badge/v2.json)](https://github.com/astral-sh/ruff)
+[![image](https://img.shields.io/pypi/v/maxgcp)](https://pypi.python.org/pypi/maxgcp)
+[![image](https://img.shields.io/pypi/l/maxgcp)](https://pypi.python.org/pypi/maxgcp)
+[![image](https://img.shields.io/pypi/pyversions/maxgcp)](https://pypi.python.org/pypi/maxgcp)
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+Maximum genetic component phenotyping. Optimized phenotype definitions boost GWAS power.
+
 `maxgcp` is a Python package that implements maximum genetic component phenotyping (MaxGCP), a method that optimizes a linear phenotype definition to maximize its heritability and genetic correlation with a trait of interest.
 In short, this method results in a phenotype definition that is, close to the genetic component of the trait of interest, on the individual level.
 This phenotype definition can be used in various applications, including enhancement of statistical power in genome-wide association studies (GWAS).
 `maxgcp` requires only estimates of genetic and phenotypic covariances, which can be obtained from GWAS summary statistics.
+
+## Usage
+
+```python
+import maxgcp
+import numpy as np
+
+# Genetic covariances between target and feature phenotypes
+genetic_cov_vec = np.array([0.5, 0.75, 0.25])
+phenotypic_cov_mat = np.array([
+    [0.5, 0.25, 0.1],
+    [0.25, 0.3, 0.05],
+    [0.1, 0.05, 0.6],
+])
+
+# Compute the MaxGCP phenotype (defined by these weights)
+w = maxgcp.fit_coheritability(genetic_cov_vec, phenotypic_cov_mat)
+
+# Evaluate MaxGCP at the individual level
+feature_phenotypes = np.array([
+    [1, 0, 0],
+    [0, 0, 1],
+    [1, 1, 1],
+    [0, 0, 0],
+])
+maxgcp_phenotypes = feature_phenotypes @ w
+
+# Show the results
+>>> maxgcp_phenotypes
+array([-0.34242555,  0.18438299,  1.87895044,  0.        ])
+```
+
+MaxGCP fits a phenotype (y) to a target (z) to maximize coheritability between y and z.
+This package can also fit a maximally heritable phenotype `maxgcp.fit_heritability` or a maximally genetically correlated phenotype (`maxgcp.fit_genetic_correlation`.
+
+## Installation
+
+```bash
+pip install maxgcp
+```
+
+`maxgcp` depends on NumPy, SciPy, and pandas.