update readme

Author: bjlittle

README.md

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+# nc-time-axis
+
+<h4 align="center">
+    Support for a cftime axis in matplotlib
+</h4>
+
+<p align="center">
+<a href="https://anaconda.org/conda-forge/nc-time-axis">
+<img src="https://img.shields.io/conda/vn/conda-forge/nc-time-axis?color=orange&label=conda-forge&logo=conda-forge&logoColor=white"
+     alt="conda-forge"></a>
+<a href="https://pypi.org/project/nc-time-axis/">
+<img src="https://img.shields.io/pypi/v/nc-time-axis?color=orange&label=pypi&logo=python&logoColor=white"
+     alt="pypi"></a>
+<a href="https://github.com/psf/black">
+<img src="https://img.shields.io/badge/code%20style-black-000000.svg"
+     alt="black"></a>
+<a href="https://github.com/SciTools/nc-time-axis/blob/master/LICENSE">
+<img src="https://img.shields.io/github/license/SciTools/nc-time-axis?style=plastic"
+     alt="license"></a>
+<a href="https://github.com/SciTools/nc-time-axis/graphs/contributors">
+<img src="https://img.shields.io/github/contributors/SciTools/nc-time-axis?style=plastic"
+     alt="contributors"></a>
+</p>
+
+
+## Installation
+Install `nc-time-axis` either with `conda`:
+```shell
+    conda install -c conda-forge nc-time-axis
+```
+Or `pip`:
+```shell
+    pip install nc-time-axis
+```
+
+
+## Example
+
+    import random
+
+    import cftime
+    import matplotlib.pyplot as plt
+
+    from nc_time_axis import CalendarDateTime
+
+    calendar = "360_day"
+    dt = [
+        cftime.datetime(year=2017, month=2, day=day, calendar=calendar)
+        for day in range(1, 31)
+    ]
+    cdt = [CalendarDateTime(item, calendar) for item in dt]
+    temperatures = [round(random.uniform(0, 12), 3) for _ in range(len(cdt))]
+
+    plt.plot(cdt, temperatures)
+    plt.margins(0.1)
+    plt.ylim(0, 12)
+    plt.xlabel("Date")
+    plt.ylabel("Temperature")
+    plt.show()
+
+![alt text](https://github.com/SciTools/nc-time-axis/raw/master/example_plot.png "Example plot with cftime axis")
+
+
+## Reference
+* [cftime](https://github.com/Unidata/cftime) - Time-handling functionality from netcdf4-python.
+* [matplotlib](http://matplotlib.org/) - Plotting with Python.