docs: Write project goals into readme (#4)

Author: kylebarron

README.md

@@ -1,2 +1,20 @@
 # async-geotiff
-Async GeoTIFF reader for Python
+
+Async GeoTIFF and [Cloud-Optimized GeoTIFF][cogeo] (COG) reader for Python, wrapping [`async-tiff`].
+
+[`async-tiff`]: https://github.com/developmentseed/async-tiff
+[cogeo]: https://cogeo.org/
+
+## Project Goals:
+
+- Support only for GeoTIFF and Cloud-Optimized GeoTIFF (COG) formats
+- Support for reading only, no writing support
+- Full type hinting.
+- API similar to rasterio where possible.
+    - We won't support the full rasterio API, but we'll try to when it's possible to implement rasterio APIs with straightforward maintenance requirements.
+    - For methods where we do intentionally try to match with rasterio, the tests should match against rasterio.
+- Initially, we'll try to support a core set of GeoTIFF formats. Obscure GeoTIFF files may not be supported.
+
+## References
+
+- aiocogeo: https://github.com/geospatial-jeff/aiocogeo