add simple build instruction

Author: leofang

cuda_py/DESCRIPTION.rst

@@ -0,0 +1,9 @@
+# `cuda.py`: (experimental) pythonic CUDA module
+
+Currently under active development. To build from source, just do:
+```shell
+$ git clone -b cuda_py https://github.com/NVIDIA/cuda-python
+$ cd cuda-python/cuda_py  # move to the directory where this README locates
+$ pip install .
+```
+For now `cuda-python` is a required dependency.

cuda_py/README.md

@@ -49,4 +49,4 @@ packages = ["cuda", "cuda.py"]
 
 [tool.setuptools.dynamic]
 version = { attr = "cuda.py._version.__version__" }
-readme = { file = ["DESCRIPTION.rst"], content-type = "text/x-rst" }
+readme = { file = ["README.md"], content-type = "text/markdown" }