docs: readme example and install

README.md

@@ -18,4 +18,32 @@ A Python package to compute and visualize observation metrics for periodic event
 In Astronomy, *portrait* is useful to answer the following questions:
 - How much of an orbit with period $P$ has been observed given certain observation times? ([tutorial](https://portrait.readthedocs.io/en/latest/coverage.html))
 - What period $P$ matches with this list of events? ([tutorial](https://portrait.readthedocs.io/en/latest/periodmatch.html))
-- How a certain target must be observed to cover all orbits with periods lower than $P$ days? 
+- How a certain target must be observed to cover all orbits with periods lower than $P$ days?
+
+Documentation at [portrait.readthedocs.io](https://portrait.readthedocs.io)
+
+## Example
+Given the range of periods you want to cover, here is how to compute the amout of phase covered by your observation times
+```python
+from portrait import coverage
+
+time = ... # your observation times
+periods = np.linspace(0.1, 10, 2000)
+
+covered = coverage(times)(periods) 
+```
+And plotting it with `matplotlib`
+```python
+import matplotlib.pyplot as plt
+
+plt.subplot(111, xlabel="periods", ylabel="coverage")
+plt.plot(periods, covered, c="0.5")
+```
+
+![image](https://github.com/lgrcia/portrait/assets/20612771/b1fdf523-c0ea-41fe-9b9f-246c9f77d7e6)
+
+## Installation
+
+```bash
+pip install portrait
+```