#1 Update README

Author: astropenguin

README.md

@@ -1,2 +1,40 @@
 # xarray-custom
+
+[![PyPI](https://img.shields.io/pypi/v/xarray-custom.svg?label=PyPI&style=flat-square)](https://pypi.org/pypi/xarray-custom/)
+[![Python](https://img.shields.io/pypi/pyversions/xarray-custom.svg?label=Python&color=yellow&style=flat-square)](https://pypi.org/pypi/xarray-custom/)
+[![Test](https://img.shields.io/github/workflow/status/astropenguin/xarray-custom/Test?logo=github&label=Test&style=flat-square)](https://github.com/astropenguin/xarray-custom/actions)
+[![License](https://img.shields.io/badge/license-MIT-blue.svg?label=License&style=flat-square)](LICENSE)
+
 :zap: Data classes for custom xarray constructors
+
+## TL;DR
+
+xarray-custom is a Python package which helps to create custom DataArray classes in the same manner as [the Python's native dataclass](https://docs.python.org/3/library/dataclasses.html).
+Here is an introduction code of what the package provides:
+
+```python
+from xarray_custom import coordtype, dataarrayclass
+
+
+@dataarrayclass(('x', 'y'), float, 'custom')
+class CustomDataArray:
+    x: coordtype('x', int)
+    y: coordtype('y', int)
+    z: coordtype(('x', 'y'), str) = 'spam'
+
+    def double(self):
+        """Custom DataArray method which doubles values."""
+        return self * 2
+
+
+dataarray = CustomDataArray([[0, 1], [2, 3]], x=[2, 2], y=[3, 3])
+onesarray = CustomDataArray.ones(shape=(3, 3))
+doubled = dataarray.custom.double()
+```
+
+The key points are:
+
+- Custom DataArray instances with fixed dimensions and coordinates can easily be created.
+- Default values and dtype can be specified via a class decorator and class variable annotations.
+- NumPy-like special factory functions like ``ones()`` are provided as class methods.
+- Custom DataArray methods can be used via a custom accessor.